Seattle Social Development Project - Results
The analysis was done cross-sectionally (comparing age 15 group status with age 15 behaviors) and longitudinally (comparing age 14 group status with age 15 behaviors). The cross-sectional results at age 15 are presented in figures 1, 2, and 3. Results from the longitudinal comparison are similar to the cross-sectional results and therefore are not presented. Figure 1 presents the mean, or average, IOR's for self-reported delinquency during the past year; figure 2 presents the mean IOR's for court-recorded delinquency. Figure 3 presents annual rates for measures of self-reported drug selling and substance use. An asterisk has been placed next to the variables for which mean delinquency rates were significantly higher for gang members than for youth with delinquent peers.
A consistent pattern of offending was found across the 3 status groups for all 11 measures of delinquency and substance use. On all measures of delinquency and substance use, rates of offending were lowest for youth with nondelinquent peers, higher for youth with delinquent peers, and highest for gang members. For example, as shown in figure 1, youth with nondelinquent peers committed an average of 1.6 self-reported acts of violent delinquency in the past year, while youth with delinquent peers committed an average of 5.1 violent acts and gang members committed more than 11 violent acts.
For this analysis, t-tests were conducted to determine whether observed differences in offending between gang members and nongang youth with delinquent peers were statistically significant. Gang members had significantly higher offense rates on 9 of the 11 measures of delinquency and substance use -- that is, at age 15, gang members committed significantly more of the following acts than nongang youth with delinquent peers (as indicated by an asterisk in figures 1, 2, and 3):
In summary, gang membership was associated with increased participation in various acts of delinquency and substance use, even in comparison with youth who associate with delinquent peers. It would thus appear that gang membership does contribute to delinquency over and above associating with delinquent peers. However, it is also possible that delinquency rates are higher among gang members because they also associate with delinquent peers. Therefore, the observed effect of gang membership may actually derive from the simple fact that gang members have a lot of delinquent friends.
To rule out this possibility, a statistical technique called structural equation modeling was used; this technique tests causal relationships among a variety of variables at the same time. It was used to examine the impact of gang membership on delinquency after controlling for association with delinquent peers. Structural equation modeling provides four kinds of information:
Specifically, the effect of gang membership on delinquency at age 15 was examined, controlling for association with delinquent friends at ages 14 and 15 and for delinquency at age 13. If gang membership provides a unique and strong contribution to delinquency above and beyond that made by associating with delinquent peers and previous delinquency, then the path coefficients from gang membership to delinquency should be significant in the causal models presented in figures 4 and 5.
The results revealed that gang membership contributed to delinquency above and beyond associating with delinquent peers and previous delinquent behavior. As shown in figure 4, the paths from gang membership at age 14 and at age 15 to self-reported general delinquency at age 15 were significant, even when associating with delinquent friends and previous delinquency were included in the model (path coefficients of 0.18 and 0.22, respectively, p<0.01). Similar patterns were found for court-recorded delinquency, as shown in figure 5.
Overall, SSDP respondents who were gang members always had the highest rates of delinquency and substance use. For 9 of the 11 delinquency and substance use measures, rates for gang members were significantly higher than those for youth with delinquent peers. In addition, structural equation modeling revealed that gang membership contributed to delinquency even after the effects of delinquent peers and previous delinquency had been accounted for.1
1 A complete description of these analyses can be found in Battin et al. (1998).