In SEM analysis, PRS was taken to the center. PRS was expected to be effective on nicotine addiction and FTND. However, the effect of PRS on nicotine addiction was not found to be significant. However, its effect on FTND was significant, even if it was weak. Whether the PRS has an effect on SES, WISDM and other types of addiction was also examined. PRS, which has no significant effect on WISDM, cocaine and opiate, exerts a stronger effect on alcohol and marijuana addiction than it does on FTND. This result supports some studies in the literature (Berrettini and Doyle 2011, Hartz and Bierut 2010). In addition, a strong effect of the PRS on the SES was observed. Although this is a statistically significant result, it is insignificant in terms of field knowledge.
The strong effect of the SES on WISDM and the significant effect of the WISDM variable on all addiction types are one of the key results of this study. These effects show that SES affects nicotine addiction motivation and that smoking addiction motivation affects not only smoking addiction but also other substance addictions. Although WISDM has been associated with FTND and alcohol addiction in the literature (Cook et al. 2012), there is no information about its association with marijuana, opiate and cocaine addiction. Here, WISDM is the mediator between SES and addiction to smoking, alcohol, marijuana, opiate and cocaine. Another key result of this study is the effect of alcohol addiction on nicotine, marijuana, and cocaine addiction. The interaction between alcohol addiction and nicotine addiction has been demonstrated in many studies (Falk et al. 2006, Tarren and Bartlett 2016). While the results obtained support these studies, they also show that alcohol addiction is a trigger for nicotine, marijuana and cocaine addiction.
When the chi-square values of the models obtained in the confirmatory factor analysis and SEM analysis are examined, it is seen that the significance level is below 0.05. This situation is interpreted as the tested model is significantly different from the data. This value is required to be above 0.05 in order to accept the model. However, it is stated in the literature that since this statistic is a sensitive statistic that is strongly affected by the sample size, it should not be taken into account in cases where the sample size is over 200, and the CMIN / DF value obtained by dividing the chi-square value by the degree of freedom should be used instead of this statistic (Marsh and Hocevar 1985). For this reason, the chi-square significance statistic was ignored considering that the model showed perfect fit according to the known threshold values of all goodness of fit statistics (Browne and Cudeck 1992, Joreskog and Sorbom 1996, Bentler 1990).
Although nicotine addiction was the focus of this study, other substance addictions were also examined and interesting results were obtained. Especially the strong effect of the SES on WISDM and the effect of the WISDM on other substance addictions besides nicotine addiction are very important in terms of showing that SES is a phenomenon that indirectly affects all substance addictions. In addition, the effect of alcohol addiction on nicotine, marijuana, and cocaine addiction has revealed the triggering effect among substance addictions. The results of this study show that certain genetic variants known to affect one type of addiction may also have an effect on other substance addictions. In addition, the motivation created by the SES for one substance addiction may also play a role in the development of other substance addictions.
This study has some limitations. First, odds ratios and the scores calculated in the PRS analysis are specific to this study and cannot be generalized. It is possible to obtain different ratios and scores with another data set. Likewise, the model and coefficients obtained by SEM analysis may not be valid in a different data set. The results obtained from this study need to be verified with different data sets in order to increase their generalizability. In future studies, it is possible to increase the number of SNPs included in the PRS analysis, to perform PRS analysis for SNPs on different genes and include them in the model to examine the effects on nicotine addiction as well as other types of addictions. In addition, by including the PRS scores calculated for different SNP groups together into the SEM model, both their interactions with each other and with the addiction types can be examined.