But let’s consider the example of teenager A, and the question that was posed: If teenager A “becomes more depressed by age 22, would we not reasonably expect their life activities to reflect their state of mind?” Of course their activities at age 22 should reflect their state of mind at age 22. But this is NOT what the study found! Instead, to extrapolate the findings to this example, the study found that what teenagers were doing AT AGE 17 was related to how depressed they were at age 22. Again, it is the associations OVER TIME that are unique to this study!

As for the opposite possibility that was mentioned: If the study had found that watching more TV in high school was associated with LESS depression 7 years later (instead of more), I would be asking why. For example, I might consider whether there is something about watching television that helps people develop ways for coping with negative emotions or life stressors. Although the study found the opposite, I don’t think this possibility is “patently absurd.”

And, again, of course no study can control for all possible variables. This study was based on data from the National Longitudinal Study of Adolescent Health; the authors of this study did not design the questions themselves (and undoubtedly would not have had the resources to collect data from such a large representative sample). Scientific research is cumulative. No study is perfect, but each study should build on and add to previous work.

Given the findings, I think we need to be asking: Why was TV and overall media use in high school related to depression 7 years later? Does TV viewing directly impact mood states in a negative way? If so, through what mechanism? Does it matter what types of television programs young people are watching (the data set did not include this information)? Or, do people who spend more time watching television communicate less with family and friends, which reduces the availability of interpersonal support? Or could it be that young people who were watching LESS television were engaged in other activities that acted as a buffer for stressful life events (e.g., more involved with extra-curricular activities or volunteer work?). These are questions that could grow out of this study, and which might yield valuable answers.

If teenager A is not depressed at 17, and then, through the normal process of growing up or through a serious of life events or whatever, becomes more depressed by age 22, would we not reasonably expect their life activities to reflect their state of mind? Would we also not reasonably expect that if we conducted a study of 10,000 depressed adults, that their TV watching amounts would be significantly higher than non-depressed adults?

Let’s also look at the opposite hypothesis… What if the study had found that depressed young adults watched *less* TV. Would there be anyone suggesting that watching less TV than average increases depression? A longitudinal study doesn’t make up for plain absurdity.

I could name a half dozen factors the researchers could not control for and did not analyze that offer legitimate possible hypotheses to explain this relationship.

I have no problems with correlational research, as long as researchers don’t draw conclusions from it. These researchers did.