Contraceptive method switching among American female adolescents, 1979

J O U R N A L OF A D O L E S C E N T H E A L T H CARE 1985;6:1-7

ORIGINAL ARTICLES

Contraceptive Method Switching Among American Female Adolescents, 1979 M A R I L Y N B. H I R S C H I P h . D . 1 A N D M E L V I N Z E L N I K / P h . D .

Better knowledge about contraceptive use in adolescents is needed if pregnancy prevention is to be improved. Data from the 1979 National Survey of Young Women were used to examine method switching once contraceptive use had begun among 449 never-pregnant young women who reported premarital intercourse more than once. Bivariate X2 tests and multivariate logit regression were used to examine factors related to switching in four analyses: overall switching; switching among those with one intercourse partner; and switching from nonmedical and medical methods separately. Frequency of intercourse and type of first method had an interactive effect on switching; length of exposure to switching, type of relationship, and reason for choosing the first method were also significant. These results suggest that providers and educators should consider the circumstances under which contraceptive methods are chosen and used by young women when counseling them as to what method may be best for them. KEY WORDS:

Adolescence Contraceptive behavior Family planning

Three surveys of females 15-19 years old were conducted in the U.S. in the 1970s to examine the knowledge, attitudes, and behavior of young w o m e n regarding sex, contraception, and pregnancy. Data from these studies show that there have been simultaneous increases in the proportion of teens who

From the Department of Gynecologyand Obstetrics, Schoolof Medicine, and the Departmentof Population Dynamics, Schoolof Hygiene and Public Health, Johns Hopkins University, Baltimore, MD. Address reprint requests to: Marilyn B. Hirsch, Ph.D., Osier 101, The Johns Hopkins Hospital, 600 North Wolfe Street, Baltimore, MD 21205. Manuscript acceptedMay 17, 1984.

have premarital sexual activity and in the proportions of sexually active teens w h o have never used contraception and w h o experience a pregnancy (1). To increase regular contraceptive use by all sexually active young women, and to provide more appropriate services to decrease the proportion of young women w h o get pregnant, a better understanding of contraceptive behavior is needed. Much research has been done on contraceptive use in the aggregate among subgroups of adolescents and on individual contraceptive behavior with respect to use at particular events, such as first and last intercourse, and the regularity of use. A more comprehensive understanding is needed. We accept Miller's (2) suggestion that " . . . contraceptive behavior can be understood adequately only when it is conceptualized as a dynamic process that changes constantly." This paper focuses on one aspect of this dynamic process: method switching after contraceptive use has begun. Few studies have examined method switching in adolescents and none have employed a statistical analysis to examine the factors related to switching. Most studies on switching have used clinic samples, examining only switching involving medical methods and excluding w o m e n w h o have never been to a clinic for contraception. In the literature, the frequency of intercourse and the method being used (3-12) are the two factors most often associated with switching. An increase in intercourse frequency leads to the use of more effective methods, and a decrease in frequency to the use of less effective methods. In general, w o m e n w h o use less effective methods (at the beginning of an observation period) are more likely to switch than those who initially use more effective methods. It has been hypothesized that method switching is associ-

© Society for Adolescent Medicine, 1985 Published by Elsevier Science Publishing Co., Inc., 52 Vanderbilt Ave., New York, NY 10017

1 0197-0070/85/$3.00

2

HIRSCHAND ZELNIK

ated with a changing level of commitment in a heterosexual relationship; an increasing commitment results in the use of more effective methods (7,13).

Methods The data used in this study are from the 1979 National Survey of Young Women, a probability sample of 15-19-year-old w o m e n of all races and marital statuses living in households in standard metropolitan statistical areas in the continental United States. The analysis was limited to all never premaritally pregnant respondents w h o had had premarital sexual intercourse more than once and had ever used contraception (26.2% of the total sample). The period of observation was from first use of a method to marriage or interview, whichever came first. Contraceptive methods were dichotomized into two types: nonmedical (condom, foam/jelly/cream/suppository, rhythm, withdrawal, douche), and medical (pill, IUD, diaphragm). The dependent variable, whether a switch occurred, was also dichotomous: it was yes (and coded "1") if a type of contraceptive method was used that was different from the type of method first used, i.e., when a young woman went from using only nonmedical methods to her first use of a medical method, or vice versa. A pattern of use for each respondent was derived from dates of first use of each contraceptive method ever used. There were a few cases where the evidence strongly suggested that a respondent had used a nonmedical method solely as a backup method to the pill. These presumed backup methods were ignored and, thus, no switch occurred for these women. On the other hand, there were a sizable number of respondents who reported the first use of a nonmedical method and a medical method in the same month and year. These cases were assumed to be switches as there was no contrary evidence. To the extent that these methods were in fact used together, the amount of switching reported here is overstated. Four analyses were done to examine different facets of the switching process; two of the analyses were done by race. In the first analysis, factors related to overall switching (i.e., switching, regardless of direction) were identified for black and white young w o m e n (the category white includes whites and other nonblacks). In the second analysis, whether switching was related to the type of relationship a young woman had with her partner was examined with the races combined. In the last two analyses, factors related to switching specifically from each

JOURNALOF ADOLESCENTHEALTHCAREVOL. 6, NO. 1

type of first method were examined. There were a sufficient number of cases to examine switching from a nonmedical first method by race, but the races had to be combined for the medical first method switch analysis. There were several steps in the determination of factors related to switching. The initial selection of factors was based on two criteria: existing literature on switching and more general contraceptive use and an intuitive assessment of questionnaire items that may not have been previously examined by other investigators. These factors can be grouped into six categories: background (religion, religiosity, SES, race); first use (age, use at first intercourse, type of method first used); frequency of intercourse (in the last 12 months); length of exposure to switching (number of months from first use to end of observation, i.e., whichever came first, marriage or interview); type of relationship with intercourse partner; and first method (reason for choosing, where first learned about, responsibility for choosing, responsibility for making sure the method was used, and where the method was first obtained). Seven of the factors were initially included in all four analyses; the others were included where appropriate. Bivariate and multivariate analysis techniques were then used to statistically test the relationships between these factors and the dependent variable. Bivariate ×2 tests were used as a screening procedure to determine which factors to include in the multivariate logit regression. This regression model was chosen because it is a more appropriate model with dichotomous dependent variables than is ordinary least squares regression (14-17). The logit regression computer program used for this research was written at Johns Hopkins University (Maguire M. A reexamination of the relationship between oral contraceptives and thrombosis. Unpublished Sc.M. thesis, Johns Hopkins University, Baltimore, MD, 1977). Two regression equations were obtained for each analysis (when the races were examined separately, there were two sets of equations). The first equation, the full model, included factors significant in the X2 analysis and possible interaction terms. Continuous variables were normalized to reduce their range and were tested for nonlinear components. If the full model was significant, the second equation, the final model, was obtained. The variables in this equation included only the significant variables from the full model. If the races were examined separately, factors significant in the ×2 for either race were included in both full models, but the final models for each race

January 1985

contained only significant factors from their respective full models. If blacks a n d whites were included in the same equation, race was included as a regression factor. The log likelihood ratio test (distributed as a ×2) was used to determine the significance of the model and the variables with more t h a n two categories. A ttest was used to determine the significance of continuous and dichotomous variables. The fit of the regression model was indicated in two ways. The first was the value of the m e a n square error (s2); a value of 1.00 indicates a good fit. The second was a goodnessof-fit procedure unique to the regression program used in this research. The latter results will not be reported because their evaluation is subjective; according to the criteria, however, all of the models herein discussed gave a good fit. Because little is k n o w n about m e t h o d switching, relationships with a probability of occurring of 0.100 or less were considered statistically significant. Only significant bivariate relationships b e t w e e n the dep e n d e n t a n d i n d e p e n d e n t variables and the results of the final models will be presented.

Results Analysis One: Overall Switching by Race The percentage of never-pregnant y o u n g black w o m e n w h o h a d a switch in either direction was 32.2%, and it was 39.8% for y o u n g white w o m e n . This difference was significant at the 0.100 level. In the bivariate analysis, type of first m e t h o d a n d frequency of intercourse were significantly related to overall m e t h o d switching a m o n g the y o u n g w o m e n of each race in the direction expected (Table 1). Those with a nonmedical first m e t h o d or high intercourse frequency were more likely to switch. Age at first use was significantly related to switching only for blacks. Those with y o u n g e r ages were more likely to switch. The relationship could not be defined with any consistent pattern for whites. Length of exposure to switching was significant for each race; in general, the longer the interval the more likely that a switch had occurred. These four variables were included in the full regression equation for each race. Significant interaction was f o u n d b e t w e e n type of first m e t h o d a n d frequency of intercourse and, therefore, an interaction term was included in the model. The final regression results for both races are s h o w n in Table 2. For both groups, the interaction term was significant and therefore the effect of each of the two vari-

ADOLESCENT CONTRACEPTIVEMETHOD SWITCHING

3

Table 1. Factors Associated with the Occurrence of a Contraceptive Method First Switch in Young Women (Bivariate Analysis by Race)

Type of first method Nonmedical Medical X2(p) Frequency of intercourse in last 12 months <12 times ---12 times

X2(p)

Black

White

Percent who had a type of contraceptive method first switch (n)

Percent who had a type of contraceptive method first switch (n)

39.2 (102) 45.9 (209) 23.5 (81) 17.5 (57) 5.13 (0.024) 15.06 (<0.001)

19.2 (104) 26.5 (113) 49.3 (75) 51.0 (143) 18.19 (<0.001) 15.76 (<0.001)

Age at first use ~14 50.0 15 35.6 16 25.5 17 32.3 18, 19 16.0 ×42(p) 8.84 (0.065) Interval from first use to end of observation <6 months 0.0 6-11 months 33.3 12-23 months 27.8 24-35 months 36.8 ->36 months 55.6 ×a4(p) 16.65 (0.002)

(32) (45) (47) (31) (25)

41.4 41.4 33.8 55.1 34.7 6.43 (0.169)a

(29) (58) (74) (49) (49)

(19) (42) (54) (38) (27)

22.9 37.1 46.2 51.6 47.5 9.89 (0.042)

(48) (62) (78) (31) (40)

aNot significant.

ables cannot be assessed. With low frequency of intercourse there was no difference in the likelihood of switching b e t w e e n r e s p o n d e n t s w h o u s e d a nonmedical and those w h o u s e d a medical first m e t h o d . However, for respondents with high frequency, those with a nonmedical first m e t h o d were m u c h more likely to switch t h a n those with a medical first method. Nonmedical first m e t h o d users with a high frequency of intercourse were m u c h more likely to switch t h a n were those with low frequency. The same trend occurred for black medical first m e t h o d users, but not for whites; whites were more likely to switch if they h a d a low frequency (results not shown). The interval from first use to e n d of observation was significantly related to switching in a positive direction. Age at first use, significant for only blacks in the bivariate analysis, was significant

4

HIRSCHAND ZELNIK

JOURNAL OF ADOLESCENTHEALTHCARE VOL. 6, NO. 1

Table 2. Factors Associated with the Occurrence of a Contraceptive Method First Switch in Young Women (Multivariate Analysis by Race) Black ~3

Constant Type of first method Frequency of intercourse Age at first use linear- componentb Interval from first use to end of observation- linear component Type of first method/frequency of intercourse (n) Log likelihood Degrees of freedom Log likelihood with only constant specified Degrees of freedom

- 1.451 0.173 2.511 0.050 -2.520

ta

White p

0.33 4.87

0.742 <0.001

2.62 -3.27 178 -89.565 173 -111.613 177

0.010 0.001

13

-0.835 -0.098 1.170 0.034 0.054 -2.272

ta

-0.17 3.66 1.91 2.94 -2.80 250 - 146.997 244 -169.030 249

p

0.865 <0.001 0.057 0.004 0.006

Significance of model -2 (log likelihood ratio) Degrees of freedom p s2

44.10 4 <0.001 1.008

44.07 5 <0.001 1.010

at-Test used to test significance of 13coefficients for dichotomous and continuous variables. Degrees of freedom are: number of observations - number of parameters estimated. bThis variable was included only in the white final model.

for only whites in the regression; for both races, this resulted from controlling for length of exposure.

cantly more likely to experience a first switch than those going steady or dating (Table 3).

Analysis Two: Overall Switching for Those with One Sexual Partner

Analyses Three and Four: Switching by Type of First Method

A separate analysis was done to specifically examine whether the type of heterosexual relationship a y o u n g w o m a n h a d with her partner affected m e t h o d switching. This included all y o u n g w o m e n w h o h a d only one partner ever and h a d the same type of relationship with that partner at first and last intercourse. The three relationships are: engaged, going steady, and dating. Of the 138 y o u n g w o m e n in this analysis, 29,7% had switched their contraceptive method. Significant in the bivariate analysis were the variables significant for overall switching as well as race and type of relationship. In addition to these variables, the full model included two interaction terms: frequency of intercourse with type of first m e t h o d , and race with type of relationship. In the final model, controlling for the other significant factors, the type of relationship between the respondent and her partner was significantly related to w h e t h e r a type of contraceptive m e t h o d first switch occurred; engaged respondents were signifi-

Whether a type of contraceptive m e t h o d switch occurred was examined for each type of first method. Miller (2) had suggested that factors specific to the contraceptive m e t h o d , the user, a n d the context of use affect contraceptive behavior. The two analyses here include factors related to these dimensions that were specific to the first m e t h o d used. Because of differences b e t w e e n medical and nonmedical methods, these factors were categorized differently for the two m e t h o d types and, thus, could be included only w h e n switching from each type was examined separately. Of the black a n d white y o u n g w o m e n w h o used a nonmedical first m e t h o d , 39.2% a n d 45.9%, respectively, switched from that m e t h o d but the difference was not significant. Of all the relationships examined in the nonmedical first m e t h o d bivariate analysis, only frequency of intercourse a n d length of exposure were significant for both races. The reason for choosing (the specific first contraceptive method) was significant only for whites (Table 4). The regression re-

January 1985

ADOLESCENT CONTRACEPTIVE METHOD SWITCHING

Table 3. Factors Associated with the Occurrence of a Contraceptive Method First Switch in Young Women with One Intercourse Partner (Multivariate Analysis) ta

Constant Type of first method Frequency of intercourse Race Type of relationship Steady Dating Interval from first use to end of observation- linear component Type of first method/ frequency of intercourse (n) Log likelihood Degrees of freedom Log likelihood with only constant specified Degrees of freedom

-0.794 0.232 1.382 0.600

X 2b

0.34 2.72 1.13 5.06

p

0.734 0.007 0.261 0.080

-1.128 -1.493 0.044

2.01

0.047

-2,839

-2.12

0,036 136 -68.377 128 -82.388 135

5

traception at first intercourse were more likely to switch) but the regression was not significant.

Discussion Our results suggest that one aspect of dynamic contraceptive behavior, method switching, can be understood in the context of sexual and previous contraceptive behavior. Use of data from a national probability sample allowed for a statistical study of whether switches occurred from medical and nonmedical methods for sexually active never-pregnant young women who had ever used contraception. Many researchers have suggested that type of first method and frequency of intercourse are two important factors in contraceptive method switching. For Table 4. Factors Associated with the Occurrence of a Contraceptive Method First Switch from a Nonmedical Method in Young Women (Bivariate Analysis by Race)

Significance of model Black - 2 (log likelihood ratio) Degrees of freedom P 82

28.02 7 <0.001 1.095

at-Test used to test significance of 13 coefficients for dichotomous and continuous variables. Degrees of freedom are: number of observations - number of parameters estimated. bLog likelihood ratio test (distributed as X2) used to test significance of categorical variables. Degrees of freedo m are the number of explicit terms in the model for the variable being tested.

sults were the same as the bivariate relationships. For each race, frequency of intercourse and length of exposure were directly related to the likelihood of switching. In addition, for whites, respondents who chose a nonmedical first method because it was the only thing available were significantly more likelyto switch methods than those who chose the method because it was believed to be more effective or because of its presumed advantages. Respondents who said it was their partner's decision to choose the method had switching rates intermediate to the two extremes but the differences were not statistically significant. ~' Twenty-one percent of all the medical first method users had a contraceptive method switch. Only two factors were significantly related to switching for medical first method users in the bivariate analysis: contraceptive use at first intercourse, and length of exposure (Table 5). Only the former was related to switching in the full regression (those who used con-

Percent who had a type of contraceptive method first Switch Frequency of intercourse in last 12 months <12 times 18.8 ->12 times 75.0 ×12(p) 30.64 (<0.001) Interval from first use to end of observation <6 months 0.0 6-11 months 38.5 12-23 months 31,3 24-35 months 50.0 ->36 months 73.3 ×42(p) 15.45 (0.004) Reason for choosing the first method Most effective 41.2 Advantages of 31.3 the specific method Partner's 39.1 decisiona Only thing 46.7 availablea X2(p) 1.58 (0.664) b

White

(n)

Percent who had a type of contraceptive method first switch

(n)

(64) (36)

26.7 60.0 22.63 (<0.001)

(90) (115)

(10) (26) (32) (18) (15)

27.5 44.0 50.0 57.1 58.6 9.21 (0.056)

(40) (50) (58) (28) (29)

(17) (32)

33.3 37.9

(18) (58)

(23)

42.5

(40)

(30)

56.0

(91)

6,56

(0,088)

aThese categories contain some other related responses. bNot significant.

6

HIRSCHAND ZELNIK

JOURNALOF ADOLESCENTHEALTHCAREVOL. 6, NO. 1

Table 5. Factors Associated with the Occurrence of a Contraceptive Method First Switch from a Medical Method in Young Women (Bivariate Analysis)

Percent who had a type of contraceptive method first switch (n) Contraceptive use at first intercourse No Yes

X~(P) Interval from first use to end of observation <6 months 6-11 months 12-23 months ---24 months

×2(p)

12.2 (49) 25.8 (89) 3.52 (0.061) 0.0 17.9 28.6 23.9 6.43 (0.092)

(17) (28) (42) (46)

each race, it was found to be an interactive, rather than an additive, effect. Frequency of intercourse was a major determinant of switching from a nonmedical first method; a high intercourse frequency was associated with switching to a medical method. In our study, this variable was not significant if the first method used was medical. In the literature, a change in frequency of intercourse is usually associated with method switching (7,10). A change could not be measured with our data; frequency of intercourse in the last 12 months before interview or marriage was used instead. The interval from first use to end of observation, i.e., length of exposure to switching, was associated with overall switching as well as switching to a medical method. The longer the interval, the greater likelihood of switching. This supports Gorosh's (6) suggestion that there is perhaps a certain amount of baseline switching. However, even controlling for this factor, other variables remain significantly related to switching. Although use of a medical method may come with long intervals, there are important determinants of switching that act independent of time. The continuous interval was not significant in switching from a medical method. Type of relationship was related to switching in the direction expected from the literature (7,13); those who were engaged were more likely to switch than those going steady or dating. This relationship also held for nonmedical first method users. Young white w o m e n w h o had an initial commitment to their nonmedical first method and showed

some forethought in choosing the method because they thought it was most effective or because of a preconceived advantage were less likely to switch than those who chose it with little forethought, i.e., because it was the only thing available. For young w o m e n who used a medical first method, those who used it at first intercourse were more likely to switch to a nonmedical method than those who delayed the first use of a contraceptive method. In their study, Zabin et al. (18) found a disproportionately high risk of pregnancy among adolescents in the six months after first intercourse. Contraceptive use not only reduced that risk but spread it more evenly over time. They concluded that this was evidence for a need to educate young w o m e n about contraception before they became sexually active. The evidence from our study suggests that more research is needed to determine what method should initially be used by these young women. Some general observations about these results can be made. None of the background factors, as defined here, were related to switching. Although important in other contraceptive behavior, they were not important in switching. It is possible that other dimensions of these or other background factors not included could be related to switching. The same may also be true of the first use variables. In our study, switching in each direction was associated with unique factors. This suggests that any discussion or examination of the determinants or consequences of switching should examine switching by direction. Switching is one form of contraceptive behavior where blacks and whites appear to have more similarities than differences. Most of the racial difference in overall method switching can be explained by differences in type of first method and frequency of intercourse. Whites had higher rates of switching because they had higher proportions of young w o m e n with nonmedical first methods and higher intercourse frequencies. Moreover, most of the important factors in switching for each race were the same. Our results suggest that providers and educators may need to consider the circumstances under which contraceptive methods are chosen and used in counseling and educating young w o m e n as to the best method for them. Medical contraceptive methods, although they can effectively protect against pregnancy, are far from ideal for all young women. If a female adolescent has good reasons for choosing a method and her circumstances are compatible with her maintaining its use, she may use that method effectively and regularly and therefore be adequately

January 1985

protected against an unwanted pregnancy. These findings support Bachmann's (19) suggestion that satisfaction and trust in a method may be necessary ingredients for successful contraceptive counseling. This research was undertaken while Marilyn B. Hirsch was a graduate student in the Department of Population Dynamics. Part of this work was supported by grant no. HD-11107 from the National Institute of Child Health and Human Development, National Institutes of Health, Department of Health and Human Services.

References 1. zelnik M, Kantner JF. Sexual activity, contraceptive use and pregnancy among metropolitan-area teenagers, 1971-1979. Faro Plan Perspect 1980;12:230-7. 2. Miller WB. Psychosocial aspects of contraception. In: Committee on Contraceptive Technology of the National Research Council, 1978. Contraception: Science, Technology and Application. Washington, National Academy of Sciences, 1980. 3. Cosgrove PS, Penn RL, Jr., Chambers N. Contraceptive practice after clinic discontinuation. Fam Plan Perspect 1978;10: 337-40. 4. Farrell C, Kellaher L. My mother s a i d . . . The way young people learned about sex and birth control. London, Routledge and Kegan Paul, 1978. 5. Foreit KG, Foreit JR. Correlates of contraceptive behavior among unmarried U.S. college students. Studies Farn Plan 1978;9:169-74. 6. Gorosh M. Patterns of contraceptive use among female adolescents: method consistency in a clinic setting. J Adolesc Health Care 1982;3:96-102.

ADOLESCENT CONTRACEPTIVE METHOD SWITCHING

7

7. Lindemann C. Birth control and unmarried young women. New York, Springer Publishing Company, 1974. 8. Margolis A, Rindfuss R, Coghlan P, Rochat R. Contraception after abortion. Fam Plan Perspect 1974;6:56-60. 9. Reichelt PA. Changes in sexual behavior among unmarried teenage women utilizing oral contraception. J Popul 1978;1:57-68. 10. Trussell J, Westoff CF. Contraceptive practice and trends in coital frequency. Faro Plan Perspect 1980;12:246-49. 11. Westoff CF, ]ones EF. Patterns of aggregate and individual changes in contraceptive practice, United States, 1965-1975. U.S. National Center for Health Statistics, Vital and Health Statistics, Series 3, Number 17, U.S. Department of Health, Education and Welfare, (PHS) 79-1401, 1979. 12. Zelnik M, Kantner JF, Ford K. Sex and pregnancy in adolescence. Beverly Hills, Sage Publications, 1981. 13. Miller WB. Sexual and contraceptive behavior in young unmarried women. Primary Care 1976;3:427-53. 14. Cox DR. The analysis of binary data. London, Spottiswoode, Ballantyne and Co. Ltd., 1970. 15. Walker SH, Duncan DB. Estimation of the probability of an event as a function of several independent variables. Biometrika 1967;54:167-79. 16. Nerlove M, Press SJ. Univariate and multivariate log-linear and logistic models. Santa Monica, Rand Corporation, R-1306EDA/NIH, 1973. 17. Mood AM, Graybill FA, Boes DC. Introduction to the theory of statistics, third edition. New York, McGraw-Hill Book Company, 1974. 18. Zabin LS, Kantner JF, Zelnik M. The risk of adolescent pregnancy in the first months of intercourse. Fam Plan Perspect 1979;11:215-22. 19. Bachmann GA. Contraceptive failure in a college population. Adv Plan Parenthood 1981;16:34-38.