Experimental Design and Methods for School-Based Randomized Trials

Design Paper Experimental Design and Methods for School-Based Randomized Trials: Experience from the Hutchinson Smoking Prevention Project (HSPP) Arthur V. Peterson Jr., PhD, Sue L. Mann, MPH, Kathleen A. Kealey, CTR, and Patrick M. Marek, MS Cancer Prevention Research Program, Division of Public Health Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington (A.V.P., S.L.M., K.A.K., P.M.M.); and University of Washington, Department of Biostatistics, Seattle, Washington (A.V.P.)

ABSTRACT: Nonadherence to accepted design principles for randomized trials has been a limitation of school-based intervention research. Designed to overcome these limitations, the Hutchinson Smoking Prevention Project (HSPP) is a 15-year randomized trial to determine the extent to which a school-based (grades 3–12) tobacco use prevention intervention can deter youth tobacco use throughout and beyond high school. This paper presents the HSPP experimental design, together with methods for its implementation, and an evaluation of the degree to which HSPP has adhered to principles of randomized trials. Results from the experimental design and its conduct include (1) a recruitment rate of 97.6% (40 of 41 targeted school districts), (2) full and active participation for the trial’s duration by 100% of the 40 school districts recruited, (3) implementation by virtually all teachers (99%⫹), with 86% implementation fidelity, and (4) outcome determination for 94.3% (7910) of 8388 original study participants identified 12 years previously at baseline. The high degree of rigor achieved by the HSPP experimental design ensures confidence in the trial’s soon-to-be available intervention effectiveness results. Equally important, for future school-based trials, the HSPP design and its execution have illustrated that school-based research can adhere to the principles of rigorous randomized trials, with high rates of implementation, and very high rates of recruitment, maintenance, and follow-up of study participants, even for studies with decade-long follow-up periods. Rigor in school-based trials can be achieved through a combination of (1) commitment to the principles of randomized trials, (2) attention to the special challenges of trials specific to the school setting, (3) adoption and meticulous execution of proven

Research for this paper supported by National Cancer Institute Grants CA-38269, CA-34847, and CA-57388. Address reprint requests to: Arthur V. Peterson Jr., Fred Hutchinson Cancer Research Center, Division of Public Health Sciences MP-603, 1100 Fairview Ave N, P.O. Box 19024, Seattle WA 98109-1024. Received April 9, 1999; accepted November 1, 1999. Controlled Clinical Trials 21:144–165 (2000)  Elsevier Science Inc. 2000 655 Avenue of the Americas, New York, NY 10010

0197-2456/00/$–see front matter PII S0197-2456(99)00050-1

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methods for trial conduct, and (4) establishment at the outset of principles for maintaining positive collaborative relationships with participating school districts for the duration of the trial. These findings are important in light of the great potential for using the nation’s schools to access youth for health promotion/risk-factor prevention. Control Clin Trials 2000;21:144–165  Elsevier Science Inc. 2000 KEY WORDS: Group randomized trials, prevention trials, school-based research, adolescent smoking prevention, attrition, children

INTRODUCTION The school setting is a promising venue for reaching youth with health promotion interventions, and indeed, school-based intervention trials are increasingly prevalent. To enable strong, unambiguous conclusions about degree of intervention effectiveness, such trials must apply the well established principles for the design and conduct of rigorous randomized trials [1–6]. These principles, adapted to the school setting, include: (1) use of the school or school district (as opposed to the classroom, or individual) as the experimental unit; (2) sample size sufficient to achieve acceptable statistical power, even (for group-randomized trials) in the presence of (intraclass) correlation of outcomes within groups; (3) high rates of recruitment of schools; (4) random assignment of intervention condition; (5) intervention fidelity (provider compliance) across schools; (6) avoidance of intervention contamination in the control condition; (7) participation by school districts for the duration of the trial; and (8) high rates of follow-up and participation in outcome ascertainment [7–11]. Reviews of tobacco use and substance abuse prevention research in the school setting have reported various experimental design and methodology deficiencies in all of these areas [7, 8, 12–22]. For example, attaining high rates of follow-up has been a problem in school-based trials. Sussman [23] reviewed 15 smoking prevention studies with average follow-up of 44 months (range: 20 to 72 months). Follow-up rates to endpoint averaged a disappointing 64% (range: 40% to 94%). Thus, on average, more than one-third of study participants were lost to follow-up in these studies. Such attrition is highly problematic because it degrades internal validity [5, 6]. Various attrition analyses are sometimes performed to document comparability of attrition with respect to experimental condition and baseline variables. However, such analyses are unable to shed light on the key piece of information needed for internal validity: the intervention impact among those lost to follow-up. As a result, the evaluation of intervention impact from only those followed up could be subject to considerable bias, because those lost could have attitudes and behaviors—and most important, an intervention impact—that differ from those who are followed [24, 25]. Another significant design problem common in school-based trials has been control condition contamination. In school-based trials, contamination of individual youths in the control condition most commonly occurs via unintended acquisition and implementation of the intervention by control teachers, or via student movement from the control to experimental condition. Both of these routes of contamination are most likely to occur when randomization is by individual classroom or school, rather than school district. Even more problematic has been the social mixing of experimental condition students with control

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condition students during follow-up. In 96% of the trials reviewed by Rooney and Murray [22], intervention condition was assigned by school, typically junior high school (or classroom). As a result, different schools within a school district had different intervention assignments. In such designs, during post-intervention follow-up the study participants make the transition from junior high school to high school, where youth from control junior high schools (i.e., those not exposed to the intervention) mix with youth from experimental junior high schools (i.e., students exposed to the intervention). Schools are a main social environment for youth, where peer and modeling influences are important, especially for smoking acquisition. Thus, such social mixing of interventionexposed students with unexposed students could be expected to mitigate any peer-group norm and social-influence effects of the intervention, and thus dilute any difference in smoking prevalence that would otherwise be observed between the intervention and control conditions. School-based trials also must address the challenges inherent in a youth study population. For example, participation in research data collection is not an innately high priority for youth. Also, follow-up of a school-age population is difficult because many youth move, change schools, drop out of school, are absent from school, or have life experiences that make follow-up especially difficult (e.g., many relocations, family/name changes, or incarceration) [8, 26–28]. Exacerbating the follow-up challenge, endpoints in school-based trials typically occur several years to a decade or more after baseline. The experience of the Hutchinson Smoking Prevention Project (HSPP) trial, presented below, is typical: 49% of the original cohort formed in 3rd grade were no longer enrolled with their classmates 10 years later at 12th grade. Thus, tracking and data collection methods that rely solely on the participating schools would not be sufficient for following a youth population. The schools themselves also present research collaboration challenges [29]: (1) Research is not a school or school-district goal. School districts are busy with their own educational priorities, facility goals, and state/national mandates. (2) The typical curriculum of any grade level is crowded; tobacco prevention, and even health, are not required courses for students at every grade level. Nor are there always teachers in place who are comfortable teaching these subjects. Moreover, teachers and principles are generally reluctant to add curricula, particularly those that don’t meet existing course objectives. (3) Interventions that are teacher-led, as opposed to research-staff-led, are subject to possible intervention failure due to poor teacher compliance and, in the control condition, teacher-initiated intervention contamination. (4) Turnover among school decision-makers (administrators and school board members) can be frequent, making it challenging to maintain the school’s knowledge, appreciation and continuing support of the research and its activities. For example, HSPP experienced an annual turnover of 13% among school district superintendents; only three of the 40 superintendents at the start of HSPP were still there at the end. (5) Schools’ record-keeping systems, on which researchers rely for planning and executing classroom data collections, and for monitoring student enrollment, attendance, and intervention exposure, are not uniform among school districts, or even among schools within the same district. (6) Student populations that at lower grade levels attend different schools within a school district often come together at higher grade levels to attend the same school. As described

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above, this can introduce into long-term school-based trials the social-mixing type of contamination whenever randomization occurs by school. Despite these many challenges, schools are an important locus for research that focuses on children and adolescents, particularly for smoking prevention studies. They provide a convenient environment for intervening with children: 95% of all children in the United States attend elementary or secondary schools [30]. Thus, it is important to address and overcome in the school setting the challenges associated with adhering to principles of rigor for randomized trials. This paper presents the experience of the HSPP in overcoming these challenges. Specifically, we (1) present the main features of the design and execution methods of the HSPP trial, (2) evaluate the results of the HSPP conduct with respect to trial rigor, and (3) discuss the potential usefulness of various design and execution features for achieving rigor in future school-based prevention trials. THE HUTCHINSON SMOKING PREVENTION PROJECT (HSPP) Background Cigarette smoking is the number-one cause of preventable death in the United States, annually killing more than 400,00 Americans [31, 32] and costing more than $50 billion in health care [33]. Almost all adult smokers started smoking during childhood or adolescence; more than 90% started by age 20 [34]. In the United States, more than one million children start smoking every year; one third of these children will ultimately die of a tobacco-related disease [35]. The HSPP trial was proposed by the Fred Hutchinson Cancer Research Center (FHCRC) in 1983, in response to a Request for Applications (RFA) from the National Cancer Institute seeking school-based intervention studies evaluating the long-term effectiveness of interventions on the prevention of habitual cigarette smoking among youth [36]. In particular, the RFA sought proposals for controlled trials with longitudinal follow-up into young adulthood, while recognizing “that experimentation in school settings with longterm follow-up is a difficult and complex task.” Further, the RFA emphasized intervention effectiveness and practicality: “The desired overall outcome of studies is interventions that are (a) cost-beneficial, (b) cost-effective, (c) durable in their effects, (d) generalizable, and (e) readily adoptable and affordable by those schools desiring them.” Accordingly, the HSPP trial was designed both to contribute to the methodology of the design and execution of randomized trials in the school setting, and to answer the following scientific question: To what extent can the grade 3–12 HSPP school-based tobacco use prevention intervention deter tobacco use, by both girls and boys, throughout and beyond high school?

HSPP study participants are 8388 children who comprised two consecutive third grade enrollments in 40 participating Washington school districts. These students were followed through elementary, junior high, and high school to endpoint determinations at senior year of high school and two years post high school.

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The HSPP intervention was designed to meet both behavioral and educational goals. It is theory-based, and extends the social influences approach [19, 21] to emphasize motivating youth to not want to use tobacco [37]. Although it is the accepted practice now [32, 35, 38, 39], it was unique to HSPP at the trial’s start in 1984 that the intervention begins early, in grade 3, before the ages of tobacco use onset, and continues through high school when students face varied and repeated pressures to use tobacco. The grade 3–12 intervention consists of (1) teacher-led tobacco (cigarettes and smokeless tobacco) use prevention curriculum units for grades 3–10, (2) teacher training, (3) self-help tobacco use cessation materials for grades 9–12, and (4) biannual newsletters for high school teachers that highlight tobacco use prevention education resources and tips for incorporating them into multi-subject classroom activities. Components target high risk youth and emphasize delivery methods that promote student interaction and involvement. Curriculum units were designed to fit diverse classroom and school settings, to be used alone or with other health or substance abuse curricula, to meet the needs and varied learning styles of all students, and to include rich educational content. The trial’s ultimate endpoint, whether or not each study participant was a regular smoker at 2 years post high school, occurs 12 years post baseline. This long-term endpoint is significant because it occurs after the main period of youth smoking initiation, and after the transition to the post-high school “real world.” The prevalence of daily smoking more than doubles between 8th grade (9%) and young adulthood (20.6%) [40, 41]. Also, Chassin et al. [42–44] have found that over 16% of all adolescents change their smoking status (either start smoking or quit) between high school and young adulthood. The trial began in 1984, all trial activities in the schools were completed in 1997, and follow-up to endpoint was completed in the summer of 1999. Publication of effectiveness results is scheduled for 2000. MAIN FEATURES OF HSPP EXPERIMENTAL DESIGN AND METHODS Experimental Design Features The HSPP trial was designed both to meet the requirements of the RFA and to overcome the various challenges inherent in school-based prevention trials summarized above. The HSPP experimental design is shown below in Figure 1. Brief descriptions of key features of the HSPP experimental design follow. The School District as the Experimental Unit Unique in school-based smoking prevention in 1984 was the choice of the school district, instead of the school, as the experimental unit. This choice permits the investigation of a multi-grade, sequential intervention that spans the elementary, junior-high, and high-school grades. It also minimizes the risk of contamination, because it eliminates the possibility of contamination between the teachers in an experimental school and those in a control school within the same district. Important as well, it avoids within-school mixing of experimental and control study participants during follow-up. Also, randomizing entire school districts, and the resulting implementation of the HSPP intervention in

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Figure 1 HSPP experimental design.

all schools in (experimental) school districts, mimics the district-wide method by which school districts usually adopt and implement curricula. To make the trial manageable, eligible school districts were those (1) with 50 to 250 students per grade level; (2) within 200 miles of the FHCRC; (3) with self-contained, stable feeder system (no planned merging with other school districts) consisting of at least one elementary school, at least one junior high school, and one high school, and (4) with grade 3 to 7 attrition of less than 35%. These eligibility criteria yielded primarily small- to medium-size school districts in suburban and rural areas, which are often under-represented in public health research.

Experimental Conditions School districts were assigned randomly to one of two conditions, experimental (HSPP intervention) or control (no HSPP intervention). No restriction was made on the health promotion or tobacco use prevention activities of the control school districts, so that schools continued to provide whatever health curricula were normally offered. The lack of restrictions placed on control schools makes

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Table 1 Statistical Power for the HSPP Trial Nominal Relative Reduction in Daily Smoking Prevalence, (pc ⫺ pe)/pc, at Full Intervention Exposure

Girls

Boys

Girls and Boys Together

40% 30% 20%

98% 86% 51%

99% 95% 65%

99% 97% 71%

the trial’s scientific question relevant to the real world: For achieving longterm reduction of tobacco use, is the experimental intervention more effective than the usual activities in the schools? Sample Size Appropriate to the School District as the Experimental Unit Forty geographically and demographically diverse Washington State school districts were included in the study. This number of school districts, which accommodates the correlation of tobacco use endpoints among students within a school district, is sufficient to attain adequate statistical power for evaluating the intervention’s effectiveness for girls and boys separately. The statistical power reported below uses up-to-date parameters obtained from the trial’s actual experience: (1) number of school districts (40); (2) number of children in the HSPP cohort (4130 girls, 4258 boys, 8388 total); (3) loss to follow-up (4.7% girls, 6.6% boys); (4) died before endpoint (14 girls, 32 boys); (5) missing endpoint data in survey instrument (27 girls; 25 boys); (6) resulting number (n) of children with endpoint data (3894 girls, 3918 boys, 7812 total); (7) prevalence of daily smoking at Plus-2 (two years after 12th grade) in the control group (26% girls; 32% boys); (8) curtailed exposure to intervention due to outmigration during the period of intervention—average fraction of full intervention exposure (0.745), conservatively assumed to influence the intervention impact in a linear fashion, and (9) intraclass (within-school-district) correlation coefficient (0.010). This intraclass correlation yielded a variance inflation factor (“design effect”) of 1.96, 1.97, and 2.94, respectively, for girls, boys, and girls and boys together. For conservatism, the power calculations do not take into account any increased power that we hoped to attain from the matched randomization of school districts. Using the above parameters, power calculations were performed (Table 1) using a standard approximate formula based on a 2-sided ␣ ⫽ .05 test comparing two proportions with correlated outcomes: Power ⫽ ⌽关√n/2 · ⌬ ⫺ 1.96兴, where ⌬ ⫽ D/S. The quantity D is the natural logarithm of the odds ratio [pc/ (1 ⫺ pc)]/[pe/(1 ⫺ pe)], and S is the square root of

冤p (1 1⫺ p ) ⫹ p (1 1⫺ p )冥 · VIF, c

c

e

e

where VIF is the variance inflation factor due to within-school-district correlation of endpoints.

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These results suggest that the HSPP experimental design with 40 school districts has sufficient statistical power for detecting effectiveness of the HSPP intervention of 30% nominal relative reduction in daily smoking prevalence at the two-years-post-high-school endpoint. Randomized Assignment of School Districts to Condition Random assignment of experimental units to intervention condition provides a highly advantageous basis of inference that requires no assumptions [45, 46], and is consequently the method of choice for intervention trials, including those in which a group (e.g., school district, community) is the experimental unit [11]. The 40 HSPP school districts were randomly assigned to the experimental condition (20 school districts) and control condition (20 school districts), as follows. Paired randomization was performed for each of 20 matched pairs of school districts. The matching was based on tobacco use prevalence, obtained just prior to randomization from a survey of high school sophomores, on school district size and on location east vs. west of the Cascade Mountains. (The latter is important because there are marked socioeconomic differences, such as level of education, occupation and population density, between the increasingly urbanized western side of the state and the largely rural eastern side.) The randomization was witnessed by two non-study FHCRC scientists. Because it is crucial, especially in group-randomized trials, that the randomized assignment be accepted by each participating school district, and that it contribute positively to building the newly established collaborative relationships with school districts, both the randomized nature of intervention assignment and its importance to the success of the study were explained in advance to school districts, both during and following recruitment. Also, immediately following the randomized assignments, the principal investigator contacted each school district superintendent to communicate the district’s random assignment and to reinforce the importance of the randomization, and each district’s role, to the integrity of the study. Two Consecutive Cohorts Study participants are the school district’s entire third-grade enrollment in two consecutive years (i.e., two consecutive cohorts). The only exclusions were children developmentally unable to learn in the usual classroom setting. Inclusion of the districts’ entire third-grade enrollments provides for a populationbased study, with associated benefits for generalizability of the results. The large study population (sample size 8388) also provides the opportunity to evaluate intervention effectiveness for girls and boys separately, important because girls and boys have distinct smoking acquisition characteristics. The choice of two consecutive cohorts in the trial helps to achieve the number of individual study participants needed for adequate statistical power, without adding additional school districts and increasing the costs of the trial. Long-term Follow-up of the Entire Cohort The HSPP follow-up is long-term (to two years post high school), and includes all members of the original cohort, including dropouts and other highrisk children. The follow-up thus includes the entire cohort, including “outmigrators” (students who changed schools, dropped out of school, or moved out

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of the school district) and regardless of post-high school path (went on to higher education, the Armed Forces, or jobs after high school). Hence, the HSPP adheres to the “follow everyone” principle [5, 6], important for minimizing bias in the evaluation (internal validity). Also, determining intervention impact is especially relevant for the subgroup of dropouts, because their smoking prevalence is much higher than that of non-dropouts [12, 47].

Biochemical Validation of Student Self-reported Tobacco Use Misreporting of tobacco use is a possibility among adolescents [48–50], especially among those exposed to an extensive intervention (social desirability effect) [51]. Therefore, to help motivate study participants to provide accurate responses, saliva specimens were collected in class from study participants immediately after the role of cotinine measurement as an objective measure of tobacco use was explained. Cotinine was measured on a random sample, both to validate self-reported tobacco use and to measure any differential misreporting of tobacco use between the experimental and control conditions.

Use of Group Permutation-based Methods for Evaluation The group-randomized assignment of experimental condition necessitates that the treatment effect be assessed against the variation in tobacco use prevalence among school districts [52, 53], as opposed to simply the variation in tobacco use among individual students. The variation in tobacco use prevalence among school districts is larger than that implied by the usual binomial model, which assumes that outcomes for individuals within a school district are independent (i.e., assumes that the intraclass correlation coefficient is zero). Whereas early prevention trials failed to appreciate this problem, more recently the unit of analysis issue has been appropriately addressed by many research groups. Evaluation of the HSPP intervention effect will use (group) randomizationbased permutation inference [54–57]. Such permutation inference has the dual advantages of (1) accommodation of non-independence of outcomes among study participants within a school district, and (2) absence of distributional or modeling assumptions. The permutation test statistic will be an appropriately weighted average of within-pair differences [58]. To maintain the model-free feature of the randomization-based permutation method, covariates will not be included in the primary analysis.

Schedule for Reporting the Design and Results of the Trial The HSPP trial is conducted in the real world with 40 demographically and geographically diverse school districts. To protect the trial from any possibility that external influences might diminish the integrity of the trial or inhibit its completion, trial policy is to wait until all trial activities with the schools (intervention implementation and endpoint data collection) are completed before publishing the trial design and results or otherwise publicizing the trial.

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Collection of Interim Data The HSPP trial collected interim data on cigarette smoking behavior from study participants at fifth, seventh, and ninth grades. Collection of interim data enabled investigation of secondary research questions about the smoking acquisition process in children [59–64], an opportunity especially welcome in light of the trial’s policy to not publish intervention impact results before the end of the trial. Collection of School District Data From surveys of school district superintendents, school principals, and classroom teachers in both experimental and control districts, data are available on characteristics of the experimental unit (school district) including demographics (e.g., average number of students per grade, average class size, mobility of the school population), tobacco use practices and attitudes among administrators, faculty, and staff, and types and extent of health promotion and tobacco use prevention activities already existing and ongoing in the schools. Trial Conduct Methods Essential for attaining trial rigor are the methods used to maintain and execute the experimental design [1]. Methods used in the conduct of the HSPP trial are described below. “Wave” Design The HSPP trial was conducted using a “wave” design in which recruitment of school districts, and all subsequent activities, were staged over three years: six districts joined the project in its first year, 14 in its second year, and the remaining 20 districts joined in its third year. This 6-14-20 wave design is a management tool intended to attain several objectives: (1) use experience gained from earlier waves to increase efficiency, improve operations protocols, and refine data instruments and curricula for use in later waves; (2) reuse from one wave to the next classroom intervention materials, and thereby effect cost savings for the project; (3) operate efficiently and attain high-quality standards using fewer staff; and (4) spread out recruitment over three years, thus enabling the principal investigator and senior managers to fully participate in school district recruitment in parallel with leading development of the intervention and other project procedures. Recruitment of School Districts The HSPP was fortunate to have a scientific question of interest to school districts, and to be part of an organization (the FHCRC) that enjoys an excellent reputation in the state of Washington. Also, involvement with research is novel for small- to medium-size school districts. Despite these favorable conditions, the challenges associated with school-based trials (discussed above) can affect recruitment. Moreover, successful recruitment for a long-term trial needs not

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Table 2 Maintenance Principles Timing Principles Plan for maintenance during the initial trial design. Initiate maintenance during recruitment.

Management Principles Make maintenance top priority. Incorporate maintenance principles into all project activities. Develop explicit maintenance procedures. Use effective management techniques. Strive for quality. Coordinate all contacts. Document all contacts.

Customer Service Principles Know each organization. Keep each organization informed. Minimize the school’s burden (“We will do it.”). Stay visible. Do what you say you will do. Demonstrate sensitivity; express appreciation; keep a positive approach. Be responsive.

only to take into account the challenges of obtaining agreement to participate, but also to have an eye to the long-term goal of post-recruitment maintenance of collaboration. Hence, we took recruitment of school districts as a challenge, and planned carefully prior to contacting our first school district. Our recruitment strategies included the following: (1) the principal investigator was personally involved in recruitment, making initial contact with school district superintendents and participating in meetings with key school district personnel; (2) presentations to schools were focused on “selling the research,” e.g., emphasizing the importance of rigorous randomized trials for answering important scientific questions; (3) we emphasized the essential role of the schools as research partners; (4) in all interactions with schools, HSPP staff demonstrated knowledge of, and sensitivity to, schools’ needs and priorities; (5) the project stated its commitment to a “we will do it” philosophy, to minimize the school’s burden wherever possible; and (6) recruitment processes were designed to be personal, motivating, and comfortable for school personnel, and to encourage frequent and open communication. Long-term Maintenance of Collaboration Maintaining positive, long-term collaborative relationships with participating school districts was essential to the success of this long-term trial. Accordingly, established at the beginning of the project, before contacting the first school district for recruitment, were “maintenance principles” (Table 2) designed to give primary consideration to the needs and interests of school districts, schools, parents, students, administrators, and teachers. Because the trial hinged on the long-term maintenance of 40 collaborations, these maintenance principles were made a project-wide top priority, and integrated into operations protocols and training procedures for all study activities. We also developed “pure maintenance” activities specifically designed to keep collaborating school districts informed of the trial’s progress, and to provide positive reinforcement for their support. These activities included regularly scheduled mailed updates (e.g., beginning-of-year letters, end-of-year letters, secretary day cards) and biennial in-person visits with key schooldistrict personnel.

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It is not unusual in randomized trials for experimental units assigned to the control group to perceive a lack of benefit in participating, and so to be at risk for dropping out or trying to acquire the intervention. In the case of HSPP, we judged this to not be a big problem, because of the high level of interest demonstrated at recruitment, and because busy (control) teachers would have little time or incentive to take the sizeable initiative needed to seek out and add the HSPP curriculum. Nonetheless, to ensure that control districts would collaborate enthusiastically, we did the following: (1) assured each control school at the start that HSPP curriculum materials would be made available to them after the HSPP cohorts completed high school, (2) emphasized at every contact the importance of the research, and the critical role of the randomized controlled design in accomplishing it, and (3) publicly acknowledged at every biennial visit with each control school district the essential role of the control condition in a randomized trial, and our sincere gratitude for their support in this often less-than-glamorous role. Methods for Increasing Intervention Provider Compliance Provider compliance has often been a problem in school-based smoking prevention interventions [14–18]. To enhance provider compliance, the intervention is designed to be practical for classroom use and easy to implement. For example, to capitalize on teachers’ existing skills, the intervention’s use of atypical or unfamiliar teaching techniques is limited. Also, teacher training is conceptualized as a behavior intervention, and emphasizes motivating the teacher-providers to want to comply. The teacher training conceptualization and details are reported elsewhere [65]. Methods for Tracking and Follow-up of Study Participants To meet our goal of locating well over 90% of the original trial cohort for collection of the 12th grade and Plus-2 endpoints, we used and extended proven methods of tracking trial participants [25, 66]. We developed a comprehensive tracking system that featured four key strategies: (1) Collection of address and other tracking information at the outset of the trial from both schools and parents. This information was updated periodically throughout the trial, and used persistently to locate and survey outmigrating cohort members. (2) Locating students by tracking the parents. (3) Use of the U.S. Postal Service’s Forwarding and Address Update Service and National Change of Address Service to obtain new addresses of parents and youth (young adults) who have moved. (4) Use of publicly available databases (e.g., State Department of Motor Vehicle records) and online people search engines on the Internet to find participants not locatable from primary sources 1–3 above. Data Collection and Informed Consent Methods Data collection goals were (1) to be sensitive to the rights, needs and requests of study participants, parents, schools, and school districts, (2) to collect complete data, and (3) to collect accurate data. To meet these goals, procedures for in-class, outmigrator, and Plus-2 data collection were designed to motivate

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participants to want to take part, to develop rapport and build trust, to assure confidential treatment of data collected, to use procedures and questionnaires that were interesting, professional looking, and easy to complete, to provide multiple opportunities for participation, including follow-up of nonresponders, and to respect and accommodate the needs and concerns of schools, parents and study participants. In-class administration of questionnaires was used for collecting the 12th grade and interim endpoints, using methods proven effective in other smoking prevention trials. Trained project data collectors administered a confidential self-report tobacco use questionnaire, and collected saliva specimens for possible cotinine analysis, after explaining the procedures to students and offering them the opportunity to decline. In the same classroom session, but after completion of the confidential tobacco use questionnaire, data collectors administered a separate, anonymous drug and alcohol use questionnaire (at 12th grade only). To obtain data from absentees, two weeks after the initial data collection data collectors conducted a “clean-up” data collection. For those absent at both the initial and clean-up in-class data collections, a structured telephone survey like the one used for the outmigrators (see below) was conducted. A key feature of the in-class data collection procedure was to inform parents in advance via an implied consent (or “passive consent”) procedure. Three weeks in advance of the data collection, HSPP mailed to parents an informational letter, co-signed by the superintendent and the principal investigator. The letter described the survey and invited parents to call toll-free if they had questions or did not want their student to participate. Such a procedure is appropriate for a student survey with no sensitive questions, and is essential for obtaining high participation rates [67, 68]. This implied consent procedure, now widely and successfully used in school-based tobacco use prevention research, and approved for this trial by the FHCRC’s Institutional Review Board (IRB), is designed to be easy and convenient by not requiring parents to sign and return paperwork for their child to participate in an activity that poses no greater than minimal risk and with which the vast majority of parents agree [68]. Thus, by being convenient for parents, this procedure was designed to both encourage parent cooperation and to enhance student participation rates. Procedures to maximize validity of data collection in class included: (1) administering the surveys entirely by study staff, with no participation by the classroom teacher; (2) giving students the opportunity to ask questions and to decline participation; (3) explaining the test for saliva cotinine and demonstrating saliva collection (using dental roll/test tube); (4) collecting the saliva specimens simultaneously with administration of the tobacco use questionnaire; (5) making no mention of the intervention; (6) emphasizing the need for accurate reports and the important role of students; (7) assuring students that all collected data are confidential (and, for the 12th grade alcohol/drug questionnaire, anonymous); (8) collecting and securing all completed questionnaires; and (9) making no advance announcement of the data collection date. Telephone surveys were used to collect data from outmigrators. Once a probable address was identified using the project’s tracking database and procedures, we sent an advance letter to the parent/guardian of outmigrators. Next,

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a trained telephone interviewer called and, with the parent/guardian’s permission (until age 18), asked the study participant to participate in a 20-minute tobacco use telephone survey. Because logistics precluded collection of saliva specimens in a mail/telephone mode, features in the advance letter and telephone script were employed to encourage accurate self reports and to increase privacy. For example, the telephone script covered the importance of the outmigrator’s honest participation and the assurance of data confidentiality. Procedures provided for numerical, rather than word, responses to survey questions to protect privacy. Sequential mailed surveys with telephone follow-up of non-responders were used at the Plus-2 endpoint [69]. Once cohort members were located (primarily through their parents), they were mailed a survey packet containing (1) a letter reminding them about the study, asking for their participation in the endpoint survey, and explaining the confidential and voluntary nature of participation, (2) the endpoint survey, (3) a $10 check as a prepaid monetary incentive, and (4) a postage-paid reply envelope. Five days later, all cohort members were mailed a reminder/thank-you postcard. On Day 16, those not yet responding to the initial mailing were mailed a new survey packet with a different cover letter and no check. Those still not responding by Day 30 were mailed a final survey packet with a letter promising $20 (refusal conversion incentive) upon receipt of the completed survey. If no response was received by Day 47, telephone calls were made in an attempt to conduct a structured telephone survey with non-responders, for which $20 was again offered. Both prepaid and refusal-conversion monetary incentives were included because they have been demonstrated to significantly increase response rates [70–72]. Biochemical Validation Methods HSPP analyzed for cotinine concentration a 12.6% random sample of specimens obtained during the 12th grade in-class data collections. The 12.6% sample was designed to detect with a probability of 90% a 4% absolute difference in misreporting fraction between experimental and control study participants. Saliva samples were submitted along with the “blind” standards (which looked similar to the study participant samples, but with known cotinine concentrations) to a laboratory willing to abide by HSPP “acceptance/rejection” criteria applied to the blind standards. Sample results were accepted only if cotinine results on the blind standards were within pre-specified limits. RESULTS Recruitment It was necessary to invite 41 eligible Washington school districts to join the trial in order to recruit our full complement of 40 school districts (97.6% recruitment rate). The 40 school districts that did join expressed their interest in the research and committed in writing to support for the duration of the HSPP trial the random assignment to intervention condition and all planned research activities.

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Long-term Maintenance of Collaborative Relationships with School Districts All 40 of the HSPP collaborating school districts participated fully for the 12-year duration of the trial. This degree of long-term maintenance (100%) was a major factor in achieving the trial’s high rates of intervention implementation (in the experimental group) and participation in endpoint data collection. Implementation Fidelity In the experimental condition, 100% of the teachers identified by their schools to teach an HSPP curriculum unit attended the inservice training. Virtually all trained teachers (⬎99%) implemented the units in their classrooms. Eightyfive percent of the teachers were directly observed by HSPP data collectors while teaching one curriculum lesson. In 86% of the lessons observed, teachers implemented the activities as outlined in the lesson plan. There was no contamination (teaching of the HSPP intervention) in the control condition. Additional implementation results, and the teacher training program that produced them, are described elsewhere [65]. Long-Term Follow-up and Participation in Endpoint Data Collection Figure 2 shows the follow-up results for the 8388 third-grade students of the HSPP trial cohort. Outcome was successfully determined for 7910 (94.3%) of the trial cohort, with 7864 (93.8%) participating in data collection at two years post high school, and with 46 (0.5%) having died before the endpoint data collection. Significantly, only eight (0.1%) of the cohort members actively declined to complete the endpoint survey. Implied Consent Procedures Parents did avail themselves of the opportunities, communicated in the parent informational letter, to call us either with questions or to decline their child’s participation. Approximately 3% of parents called with questions, and 0.1% of parents called to decline their child’s participation. The tone of the communications was overwhelmingly positive. Only three parents (0.04%) called the project to express a preference that the consent procedure be active rather than passive. DISCUSSION AND CONCLUSIONS Despite the many challenges associated with working with schools and a youth study population, the principles of randomized trials can be adhered to with excellent results in the school setting. The 15-year experience of the HSPP randomized trial has demonstrated that meticulous application of proven methods for trial conduct, available from the published literature and adapted to the school setting, can result in (1) school districts accepting and maintaining their randomized assignment to intervention condition, (2) long-term school district cooperation and participation in research activities, including teacher compliance in experimental districts, and (3) follow-up and data acquisition rates well above 90% of the original cohort.

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Figure 2 Participation in endpoint data collection after 12 years of follow-up (followup as of 8/31/99).

The HSPP experience suggests four design features and six methods for the successful conduct of rigorous group-randomized trials in schools. Design: (1) choice of school district as the experimental unit; (2) randomized assignment of intervention condition; (3) acknowledgement of the intraclass correlation in both sample size determination and evaluation method; and (4) commitment to follow the entire cohort to endpoint. Methods: (1) recruitment procedures that promote school district collaboration for the trial’s duration; (2) development and use of explicit principles for maintaining productive, long-term collaborations with school districts; (3) meticulous application of proven tracking and data collection methods to obtain participation rates exceeding 90%; (4) inclusion of motivational components in teacher training to maximize compliance; (5) use of implied consent procedures when appropriate, both to maximize participation rates and to maximize sensitivity and convenience to busy parents; and (6) phase-in of activities by wave. One notable result from the HSPP trial is the 94% rate of follow-up/endpoint data collection participation at the final endpoint, twelve years after the study population was identified as third graders. Determination of this 94% figure uses the entire original third grade cohort as the denominator, including students who subsequently moved away from the school district, dropped out of

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school, died prior to the data collection, or were developmentally unable to participate in data collection. We judge the collection of tracking information from parents at the start of the trial to be the single most important follow-up strategy contributing to this result. The initial tracking contact with parents helped in two important ways: (1) it provided the project with reliable information for subsequent tracking of study participants, and (2) it helped us establish at the start cooperative relationships with parents—relationships that, years later, enabled us to successfully enlist parents’ help in locating study participants for post-high-school endpoint data collection. Our experience also confirmed the wisdom of seeking implied consent from the parents for collection of confidential data from study participants, provided the data instrument and procedures pose no greater than minimal risk—i.e., that survey items not ask the child about illegal activity (e.g., illegal drug use, or underage drinking), or about the parents (e.g., parental smoking practices, household income, etc.). The implied consent procedure not only maximizes participation of study participants, as is now widely known [67, 68], but is also easy and convenient for parents: in contrast to active consent, parents are not required to take time to fill out a form, sign it, and return it in order for their child to participate. In more than 10 years experience with follow-up and multiple data collections among over 8000 children, only three parents expressed dissatisfaction with the implied consent method. It is crucial for the viability of school-based research that investigators, and IRBs, recognize the important advantages of implied parental consent procedures in these circumstances, both for the research and for the parents. It should be emphasized that with an implied consent procedure comes important requirements. One, already mentioned, is that the data collection instrument and procedures be no greater than minimal risk. Another is that a convenient, no-cost-to-the-parent method of contacting the project (e.g., tollfree telephone number) be established and communicated to the parent. The third is secure procedures for delivering the informational letter to the parent address. Such procedures could include, for example, mailing informational letters directly to parents at least three weeks in advance of the data collection, and then checking returned letters at the return address (the project or the school district), and removing from the data collection roster each student for whom the informational letter to the parent was returned undelivered. Not acceptable are procedures that place the burden for letter delivery on the classroom teacher, or that involve the children carrying the letter home. Group interventions like the HSPP have great potential for public health impact, because their mass delivery and broad reach make for efficient interventions with low cost per individual reached. But the group-randomized trials needed to evaluate the effectiveness of such group interventions are inherently expensive, because the positive intraclass correlation within group means that a moderate number of entire groups is needed, which necessarily involves many more individuals than clinical trials evaluating one-on-one interventions. Therefore, given their inherent expense it is especially important that grouprandomized trials be rigorous, so that the large investment in a trial is not diminished or wasted by a degraded integrity. Indeed, the cost in diminished integrity of not keeping all groups in the study, for example, or of not achieving high follow-up rates, is much greater than the cost of achieving them. Thus,

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the additional expense needed to achieve rigor, which we judged to be small relative to the total cost of the trial, seems clearly warranted and needed to ensure the integrity of these important trials. There are several possible limitations of these results. First, there is the possibility that recruiting schools and conducting school-based research may present more and different challenges in the future than those encountered by the HSPP. That schools were viable settings for rigorous intervention trials was demonstrated by this trial for the period 1984–1999. But should the present trend continue for schools to assume additional societal responsibilities, and curricula to be more crowded, it is possible that these favorable results might not be as applicable to future years. Nonetheless, our judgment is that challenges to school-based research can be overcome in the future as well, through (1) an awareness of the challenges, (2) attention from the trial’s outset to maintenance of the school district’s long-term collaboration, and (3) sensitivity to the characteristics, needs, and situations of individual school districts. Another potential limitation is the inclusion of predominantly Caucasian students and rural school districts in the HSPP trial. We would expect that in predominantly minority populations or urban school districts the obstacles to schools’ participation would be different and, perhaps, greater. It is possible that these factors may limit the generalization of our findings. However, it seems to us more conceivable that awareness of, and special attention to, whatever needs and situations exist in the school districts and schools involved could overcome potential obstacles in urban school districts as well. Finally, the HSPP scientific question concerns the prevention of youth smoking, the number-one cause of preventable premature death in our nation. Admittedly, this provided the trial with a great societal cause, which undoubtedly both aided the recruitment of school districts and played a positive role in keeping the investigators, managers and school districts together and dedicated to seeing this long-term trial through to its completion. The HSPP’s considering at the outset the problems and challenges associated with school-based trials as identified in the literature, and its meticulous attention to experimental design and trial conduct, paid off in a study that was relatively problem-free. The problems encountered were minor; it was unnecessary to modify the design or methods to solve them. Thus, from the HSPP experience, we would judge the design features and methods presented to be robust for resolving unanticipated problems that might arise in schoolbased research. In conclusion, the experience of the HSPP demonstrates that rigorous grouprandomized trials can be conducted in schools with their full participation for a decade and longer, and with very high rates of follow-up and data collection. Providing confidence that our experience may be generalizable to other school districts throughout the nation are (1) HSPP’s large number of demographically and geographically diverse school districts with their wide variety of characteristics (style of leadership, rapport with community, morale) and their stimulating variety of periodic challenging happenstances, (2) HSPP’s large study population of children with diversity in socioeconomic status, personality, academic ability, and family situation, and (3) the extended duration of the trial. The results of the trial design and execution presented here have two highly beneficial implications. First, the implication for the HSPP trial itself is that the

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integrity attained by the HSPP will yield intervention-impact results (scheduled for 2000) that will have a high degree of validity. Second, a favorable implication for the future of school-based intervention research is the demonstration that experimental design rigor in long-term group-randomized trials can indeed be achieved in the school setting through a combination of (1) commitment to the principles of rigorous trial design, (2) attention to the special challenges of prevention trails in the school setting, and (3) adoption and meticulous execution of proven methods for trial conduct. We acknowledge with deep appreciation the children (now young adults), parents, teachers, administrators, and school staff who participated in this trial, and the leadership, support and collaboration of the 40 participating Washington school districts: Adna, Anacortes, Arlington, Bainbridge Island, Blaine, Cashmere, Castle Rock, Chimacum, Concrete, Darrington, Eatonville, Ephrata, Fife, Granite Falls, Kittitas, Lake Chelan, Lynden, Meridian, Mount Baker, Naches Valley, Napavine, Nooksack Valley, North Mason, Orting, Port Townsend, Rainier, Raymond, San Juan Island, Sequim, South Whidbey, Stanwood, Sultan, Tahoma, Toutle Lake, University Place, Vashon Island, Warden, Washougal, Winlock, and Woodland. Contributing to the initial experimental design, and providing wise counsel throughout, were Ross L. Prentice, Maureen M. Henderson, and Terry Janicki. Contributing to methods for recruitment, maintenance, and curriculum implementation in the school setting were Carl Nickerson and Robert Collins. Also contributing to the experimental design and methods were the trial’s scientific consultants: J. Allan Best, K. Stephen Brown, David Murray, Vaughn Call, and Don Dillman. Members of an external advisory panel for minimizing contamination were Donald Iverson, David Murray, and Terry Pechacek. Invaluable encouragement and counsel was generously provided by the trial’s NCI Project Officer, Thomas J. Glynn. Finally, Ross Prentice and Mark Thornquist reviewed and provided helpful suggestions on this manuscript. This trial was supported by grants from the National Cancer Institute: RO1CA-38269, PO1-CA-34847, and RO1-CA-57388, and by a donation from the Northern Life Insurance Company.

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