Why you might want to ignore everything I post on this blog, part 2:

I posted before about why you might want to ignore everything I post on this blog. Here’s a fun study that shows how connections can be drawn between silly or impossible things:

Objective To investigate whether “network effects” can be detectedfor health outcomes that are unlikely to be subject to networkphenomena.

Design Statistical analysis common in network studies, suchas logistic regression analysis, controlled for own and friend’slagged health status. Analyses controlled for environmentalconfounders.

Setting Subsamples of the National Longitudinal Study of AdolescentHealth (Add Health).

Participants 4300 to 5400 male and female adolescents who nominateda friend in the dataset and who were both longitudinally surveyed.

Measurements Health outcomes, including headache severity, acneseverity, and height self reported by respondents in 1994-5,1995-6, and 2000-1.

Results Significant network effects were observed in the acquisition of acne, headaches, and height. A friend’s acne problems increased an individual’s odds of acne problems (odds ratio 1.62, 95% confidence interval 0.91 to 2.89). The likelihood that an individual had headaches also increased with the presence of a friend with headaches (1.47, 0.93 to 2.33); and an individual’s height increased by 20% of his or her friend’s height (0.18, 0.15 to 0.26). Each of these results was estimated by using standard methods found in several publications. Afteradjustment for environmental confounders, however, the resultsbecome uniformly smaller and insignificant.

Conclusions Researchers should be cautious in attributing correlations in health outcomes of close friends to social network effects, especially when environmental confounders are not adequately controlled for in the analysis.

Source: “Detecting implausible social network effects in acne, height, and headaches: longitudinal analysis” from BMJ 2008;337:a2533

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