Table 3.
Twin Correlations and relationships between ASI and sexual risk outcomes within twin pairs before and after controlling for propensity score.
| RASB Outcome Variable | rfMZ | rDZ | MZ Twins | DZ Twins | ||
|---|---|---|---|---|---|---|
| Model (B, SE) | Model (B, SE) | |||||
| Without Propensity Score | With Propensity Score | Without Propensity Score | With Propensity Score | |||
| n of pairs | 158 | 128 | ||||
| Past year number of regular partners | ||||||
| Twin Correlation | .17 | .13 | ||||
| ASIB | 19 (.07)** | .18 (.10) | .12 (.10) | .13 (.13) | ||
| ASIW | −.03 (.10) | −.14 (.14) | .08 (.12) | −.04 (.15) | ||
| Zygosity* ASIW | .10 (.16) | −.10 (.21) | ||||
| Propensity Score | −.01 (.03) | |||||
| Past year number of casual partners among men | ||||||
| Twin Correlation | .32* | .01 | ||||
| ASIB | .68 (.17)*** | .57 (.18)** | .49 (.25) | .36 (.26) | ||
| ASIW | .78 (.30)** | .79 (.30)** | .46 (.30) | .40 (.30) | ||
| Zygosity* ASIW | −.33 (.42) | −.39 (.42) | ||||
| Propensity Score | .10 (.06) | |||||
| Past year sexual behavior under influence of drugs/alcohol among men | ||||||
| Twin Correlation | .10 | −.11 | ||||
| ASIB | .38 (.16)* | .38 (.18)* | .30 (.24) | .30 (.25) | ||
| ASIW | .50 (.26) | .50 (.26) | .76 (.26)** | .76(.26)** | ||
| Zygosity* ASIW | .26 (.37) | .26 (.37) | ||||
| Propensity Score | .00 (.05) | |||||
| Past year sexual behavior under influence of drugs/alcohol among women | ||||||
| Twin Correlation | .44** | .21 | ||||
| ASIB | .25 (.09)** | .01 (.15) | .16 (.12) | −.02 (.19) | ||
| ASIW | .03 (.11) | −.01 (.18) | .14 (.13) | .34 (.22) | ||
| Zygosity* ASIW | .11 (.17) | .34 (.28) | ||||
| Propensity Score | .04 (.05) | |||||
| Lifetime casual partners among men | ||||||
| Twin Correlation | .26* | .14 | ||||
| ASIB | .70 (.17)*** | .64 (.17)** | .25 (.23) | .19 (.24) | ||
| ASIW | .40 (.23) | .41 (.23) | .12 (.24) | .10 (.24) | ||
| Zygosity* ASIW | −.28 (.31) | −.32 (.31) | ||||
| Sexual opportunity | .49 (.10)*** | .46 (.10)*** | ||||
| Propensity Score | .07 (.05) | |||||
| Early Pregnancy | ||||||
| Twin Correlation | .14 | .04 | ||||
| ASIB | 1.82(.22)*** | .94 (.37)** | 1.59(.31)*** | 1.17 (.64) | ||
| ASIW | −.11 (.34) | −.52 (.54) | .34 (.41) | −.08 (.61) | ||
| Zygosity* ASIW | .45 (.53) | .44 (.81) | ||||
| Gender | −.74(.15)*** | −.97(.26)*** | ||||
| Propensity Score | .50 (.14)*** | |||||
Abbreviations: MZ, monozygotic; DZ, dizygotic; ASI, adolescent sexual initiation; early pregnancy: having been pregnant or having made someone pregnant before age 20 (coded yes/no); sexual opportunity: current age - time at initial sexual experience. All variables but early pregnancy (which was categorical) were z-scored. Unstandardized regression weights are presented. If ASI failed to predict an outcome in the individual-level model, we did not use that variable as an outcome measure in the discordant twin models (number of lifetime partners). If the ASI x Gender interaction was significant and ASI predicted the outcome for both genders, we report the results of the discordant twin model separately for each gender. If the ASI x Gender was significant and ASI predicted the outcome for only one gender, we report the results of the discordant twin model for that gender only. The first model termed “without propensity score” is a discordant twin model, testing the within-pair (ASIW) and between-pair (ASIB) effects on the outcomes among MZ and DZ twins. In this model, zygosity*ASIW tests whether the within-pair effect is significantly different across zygosity. The second model, termed “with propensity score” is identical to the first one, except for the addition of the propensity score. The former model included both the younger and older cohort, whereas the latter included only the younger cohort, as propensity score variables were available only for that cohort. Propensity score is identical for MZ and DZ pairs; thus, it is presented only once per model (in MZs).
<.05;
< .01;
< .001.