EXAMPLE 6 Bullying and depression

A recent study in the United Kingdom examined data on 3898 participants in a large observational study for which they had information on both victimization by peers at age 13 and the presence of depression at age 18. The researchers also had information on lots of variables, not just the explanatory variable (bullying at age 13) and the response variable (presence of depression at age 18). The research article said:

Compared with children who were not victimized those who were frequently victimized by peers had over a twofold increase in the odds of depression. . . . This association was slightly reduced when adjusting for confounders. . .

That “adjusting for confounders” means that the final results were adjusted for differences between the two groups. Adjustment reduced the association between bullying at age 13 and depression at age 18, but still left a nearly twofold increase in the odds of depression.

Interestingly, the researchers go on to mention that the use of observational data does not allow them to conclude the associations are causal.