Tuesday 19 February 2013

Underlying type

Does alcohol or drug use lead to a whole pile of other risk-taking activities, does some common underlying risk preference determine both substance abuse and other risky behaviours?

The Dunedin Longitudinal Survey group finds evidence that women with more sexual partners are more likely to later report substance dependence disorders than those with fewer partners. Women having had more than 2.5 sexual partners per year between the ages of 18-20 are 9.6 times more likely to report substance dependence disorders at age 21, adjusted for prior disorder incidence. Women aged 26-31 having had more than 2.5 partners per year are 17.5 times as likely to report substance dependence disorder at age 32. Similar patterns held among males, although the risk ratios were much smaller. 
The explanation for the relationship is likely to be complex. Four possibilities are proposed. First, sexual risk taking and substance use may be part of the cluster of risk taking behaviors common in adolescence and young adulthood (Arnett, 1992; Boyer et al., 2000; Caspi et al., 1997; Desiderato & Crawford, 1995; Donovan & Jessor, 1985; Taylor, Fulop, & Green, 1999). For instance, people who are impulsive may be more likely to engage in both activities and, consequently, more likely to become substance dependent. Second, occasions of substance use are opportunities for sexual behavior because of its disinhibitory effects and lack of accurate perception of risk (Crowe & George, 1989; Fromme, D’Amico, & Katz, 1999). Weinhardt and Carey (2000) have suggested, in a review of event-level research on this topic, that the association, especially with condom use, is also complex. Thirdly, shared context may be an important factor, insomuch as young people are likely to meet new sexual partners in situations where alcohol is served. These settings might encourage sexual behavior and facilitate multiple partnering.
The fourth intriguing possibility is that it is something about having multiple sex partners itself which puts people at risk of substance disorder. For instance, it may be due to the impersonal nature of such relationships. Or, it might be that multiple failed relationships create anxiety about initiating new relationships. Self "medication" with substances may be one way of dealing with this interpersonal anxiety (Khantzian, 1997; Stoner, George, Peters, & Norris, 2006).
They also note the studies showing that alcohol use correlates with more risky sexual practices; I didn't see reference to the one suggesting drinking was associated with more positive consequences of sex.

I'd also worry about cohort attrition effects: if men and women who are more psychologically stable are more likely to get married before the age of 30, then the pool of women reporting >2.5 sexual partners per year* between the ages of 26-31 is probably different from the pool of women reporting the same numbers in their early 20s [recall that the Dunedin study follows a cohort born in 1972-1973]. 9.5% of women reported 2.5+ partners per year at 18-20; that dropped to 4.5% by age 21-25 and to 1.7% - 8 women - by age 26-31.

I wish that the Dunedin study had some calibrated measure of risk tolerance, like the Holt and Loury measure, as well as a measure of individual discount rates. I would love to see pinned down what portion of risk-taking behaviour comes down to heterogeneity in individual risk tolerance, what portion comes down to that things with longer term costs might be disproportionately preferred by those who avoid the tyranny of the later-self, and what portion might be due to amplification effects where doing one risky thing actually does make you more likely to do another risky thing.

But the takeaway here is that studies suggesting drinking is associated with riskier sexual activity might well worry about reverse causation or common underlying causes.

* No, you can't have half a sexual partner. They're asked number of partners and that's averaged across the age range for that respondent. 


  1. I have not read the paper, but based on the abstract, it seems that they have run three different analyses, each time regressing alcohol problems on previous sexual behaviour. The obvious thing to do, given that this is a panel, would be to run a fixed effects regression, and test whether deviations from the mean of sexual partners during one period of time is associated with alcohol problems at the point in time following that period. That would automatically control for latent traits as well as other stable qualities of the subjects and their environments.

    Or am I misreading the abstract?

  2. Then I would suggest that theirs is not the analysis you want to run and would guess that if you run the analysis as described above (plus some controls), significance disappears.

  3. I heard one of the study authors on the Panel a few days ago and I was left wondering about the direction of causation and whether in fact there was any... seems to me they may be looking for an answer rather than finding and answer...

  4. Really hard to tell as it's effectively impossible for those outside the Dunedin group to get access to the Dunedin longitudinal data.

  5. At least this study notes that other underlying traits may be behind the correlation, even referencing an earlier Dunedin study that argued that pre-existing temperament and personality predicted a number of different health-harming behaviors ;)
    Also: Since their "outcome" measure is a sum of alcohol and cannabis dependence, this also adds to the indications of selection in their IQ-cannabis work.

  6. It'll be interesting to see what happens if their data is ever made public... how much will stand replication and robustness checks.