Mental Health Trajectories and Their Predictors: Application of Latent Growth Mixture Modeling in the Millennium Cohort Study

Mental Health Trajectories and Their Predictors: Application of Latent Growth Mixture Modeling in the Millennium Cohort Study

714 ABSTRACTS (ACE) METHODS: Mathematical models of causal probability as a function of time were developed describing the temporal proximity betwee...

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714

ABSTRACTS (ACE)

METHODS: Mathematical models of causal probability as a function of time were developed describing the temporal proximity between a suspected trigger event using biologic decay or Gaussian functions and the outcome, taking into account ambient-risk (rate effect) and coincidence (random time point within a diminishing fixed period). Odds ratios over time were determined to assess dynamic trigger to ambient-coincidence probabilities of hypothetical injury, disease, and death causation. RESULTS: Overall, odds ratio functions reflect a generalistic inversesquared relationship with time. This mathematical framework facilitates a direct application of parameters drawn retrospectively from the literature, individual cases, or prospective predictions. CONCLUSION: Although developed for a temporal description of influence, cross-over applications for spatial characterization are possible to create a temporospatial approach to causation. Applications to the medicolegal setting may be valuable as judgments are based on moreprobable- than-not findings which can be construed as definitive shifts between inductive and abductive reasoning.

P65 A METHOD OF COMPUTING INCIDENCE RATES WITH PARTIAL CASE REVIEW J Slezak, on Behalf of the Gardasil Safety Study Team, Department of Research and Evaluation, Kaiser Permanente Southern California, Pasadena CA; Division of Research, Kaiser Permanente Northern California, Oakland CA; Department of Epidemiology, Merck Research Laboratories, West Point, PA

PURPOSE: We sought to estimate the incidence of several autoimmune conditions in a female population who received the HPV4 vaccine. Administrative data may contain inaccurate coding, while chart review of all cases may not be feasible. We propose a method to accurately estimate incidence using administrative data and case review for a sample. METHODS: Suspected incident cases were electronically identified using ICD-9 codes, lab results, and prescriptions related to the condition. A random sample of charts was reviewed to confirm the diagnosis. Multiple imputation, using a Monte Carlo model in SAS PROC MI, was used to estimate whether non-reviewed cases would have been confirmed. Predictors included age and ICD-9 code, lab, or drug used to identify the case. 500 imputed datasets were created, with incidence rates computed in each, giving a distribution for the estimated incidence rate. RESULTS: The model accounted for differential case confirmation rates by age and method of identification, yielding incidence rates closer to published data than administrative data alone. For rheumatoid arthritis, our method estimated 4.9 cases per 100,000 person-years, vs.

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9.6 using administrative data and 5.7 in a published study of a similar population. CONCLUSIONS: This method may be useful for computing incidence when full case review is not feasible. P66 CAN RESPONDENT DRIVEN SAMPLING BE USED TO RECRUIT HOMOGENEOUS SAMPLES OVER TIME? J Risser, A Cates, A Sayegh, University of Texas School of Public Health, Houston, TX

PURPOSE: We compare injection drug users (IDU) recruited through respondent driven sampling (RDS) during the first two IDU cycles of the National HIV Behavioral Surveillance Project (NHBS). Our goal is to determine if the samples are homogeneous on basic characteristics, so that they may be considered to be from the same target population. METHODS: Data are from the Houston Texas site of NHBS-IDU1 (2005) and IDU2 (2009). Adjusted population prevalence estimates are calculated using RDSAT, adjusting for design effect and sampling characteristics. Estimates were compared using the Mantel Haenszel test for heterogeneity. RESULTS: Comparing IDU1 to IDU2, we found similar population estimates (p for heterogeneity O0.05) for age 40 to 49 years (39%/37%), Black race (73%/71%), current health insurance (33%/34%), and currently homeless (71%/67%). The populations differed (p for heterogeneity !0.05) by the proportion that: graduated from high school (54%/66%); had income greater than $5,000 (42%/60%); were arrested in the last year (28%/37%); and visited a doctor in the last year (47%/63%). The two samples also differed in the percent reporting previous HIV testing (76%/89%). CONCLUSION: Using RDS to assess behavior changes over time will be difficult if the study samples do not represent a fixed population. We looked at variables we thought would be stable over the two cycles and were surprised to find instability; we did not expect to find an increase in reported income or doctor visits. With these differences, we cannot attribute the observed increase in HIV testing solely to prevention efforts that occurred between the surveillance cycles.

P67 MENTAL HEALTH TRAJECTORIES AND THEIR PREDICTORS: APPLICATION OF LATENT GROWTH MIXTURE MODELING IN THE MILLENNIUM COHORT STUDY J Horton, T Powell, G Bonanno, A Mancini, C LeardMann, E Boyko, T Wells, T Hooper, G Gackstetter, T Smith, for the Millennium Cohort Study Team, Naval Health Research Center, San Diego, CA

PURPOSE: Little prospective research exists to explain how trauma symptoms vary across time, or about the

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proportion of US military personnel that evidence a stable pattern of symptom-free or healthy adjustment to combat deployment. Applying latent growth mixture modeling (LGMM) to the Millennium Cohort study may detect latent health trajectories and previously unnoticed subpopulations at risk for posttraumatic stress disorder (PTSD) and significantly contribute to our understanding of this condition. METHODS: Data were from 2,780 Millennium Cohort participants who completed three questionnaires between 2001 and 2008 and deployed once between baseline and the first follow-up. LGMM was used to reveal PTSD trajectories and determine covariates that best predicted class membership. RESULTS: After examining unconditional trajectory models with 1 to 6 classes, the 4-class solution was determined to fit the data best. The four symptom trajectories were: stable, low distress (83.9%), improving (7.8%), chronic posttraumatic stress (6.2%), and continuous distress (2.1%). CONCLUSION: Identifying characteristics of stability, continuous distress, and other patterns of stress response may help target non-resilient groups for early intervention. Findings may also strategically frame areas for future research, including related exposures of co-morbid symptoms and medical conditions.

P68 BUILDING CAPACITY FOR EPIDEMIOLOGIC MODELING: EXPERIENCES OF THE NAADSM DEVELOPMENT TEAM A Reeves1, N Harvey2, C Dube´3, KM Forde-Folle4, SP Case1, BA Corso4, AE Hill1, WB McNab5, R Hupalo1, CAP Reeves6, J Rooney4, J Sanchez7, A Schwickerath1, MD Salman1, 1Colorado State University, Fort Collins, CO, 2University of Guelph, Ontario, Canada, 3Canadian Food Inspection Agency, Nepean, Ontario, Canada, 4United States Department of Agriculture, 5 Province of Ontario, Ontario, Canada, 6Reeves Digital Development, Loveland, CO, 7University of Prince Edward Island, Charlottetown, Canada

PURPOSE: Among the challenges faced by epidemiologic modelers are the limited exchange of models among researchers; the lack of transparency and ambiguity in published descriptions of models; and the difficulty associated with recreating models and reproducing their findings. Here we describe measures adopted by the North American Animal Disease Spread Model (NAADSM) Development Team to address these challenges. METHODS: NAADSM is a model for the simulation of the spread and control of exotic animal diseases in naı¨ve livestock populations. NAADSM is freely available via the Internet at http://www.naadsm.org, with all related documentation and complete computer source code. The NAADSM Development Team has emphasized the

ABSTRACTS (ACE)

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production of documentation that is complete, clear, and understandable for others in the field. Programming practices used emphasize the production of readable and adaptable code. RESULTS: This open approach has fostered the growth of an international community of hundreds of modelers applying NAADSM to many different problems with significance for veterinary epidemiology and public health. CONCLUSION: We suggest that it may be useful for other investigators to emulate this open approach, to further facilitate the development, use, evaluation, and comparison of models and results of modeling studies.

P69 ASSESSMENT AND APPLICATION OF THE MULTISTATE LIFE TABLES APPROACH TO MODELING POPULATION HARM REDUCTION WITH SMOKELESS TOBACCO S Sulsky, A Bachand, G Curtin, J Swauger, ENVIRON International Corp., Amherst, MA; Colorado State University, Fort Collins, CO; R J Reynolds Tobacco Co., Winston-Salem, NC

PURPOSE: To identify and evaluate assumptions underlying the multistate life tables approach for estimating differences in population life expectancy due to different distributions of harmful exposures. METHODS: A published analysis that used multistate life tables to calculate life expectancy under different exposure scenarios was carefully evaluated to delineate source data and underlying assumptions; efforts were undertaken to replicate and improve analysis findings using US data. RESULTS: Limitations of the published analysis included risk estimates from one population applied to a dissimilar target population, resulting in lower risks for exposed than unexposed in some groups; use of identical input risk estimates for dissimilar diseases, resulting in invalid effect sizes; and failure to account for time dependent effects of exposure and removal from exposure, resulting in overestimated effects. Nevertheless, efforts to replicate analysis findings and address potential limitations yielded comparable estimates of differential life expectancies based on different exposure scenarios. DISCUSSION: While the life tables approach can provide important information regarding population life expectancy under different exposure scenarios, clear documentation and/or modification of underlying assumptions for testing the effect of alternate assumptions can be problematic. Subsequent efforts have been directed towards improving estimates of exposure-related life expectancy through dynamic simulation models that will allow for additional user-specified inputs.