A pair of social scientists from UCSD and Yale conducted drawing on data from the Gallup Panel Social Network Study combined with "objective measures of Facebook use" and self reported data for 5,208 subjects, and concluded that increased Facebook use is causally linked with depression.
The authors argue that because they drew on longitudinal data, they could rule out the possibility that depressed people turn to Facebook - rather than Facebook use causing depression.
The associations between Facebook use and compromised well being may stem from the simple fact that those with compromised well being may be more likely to seek solace or attempt to alleviate loneliness by excessively using Facebook in the first place. The explanation made our head spin.
"The longitudinal models accounted for well-being measures in wave when including Facebook use to predict the well-being outcomes in wave t + 1. Also, in our final models, we included degree (or real-world friendship counts) to adjust for this possibility, and the results remained intact. This provides some evidence that the association between Facebook use and compromised well-being is a dynamic process. Although those with compromised well-being may be more likely to use Facebook, even after accounting for a person's initial well-being, we found that using Facebook was associated with a likelihood of diminished future well-being. The exception to this is the case of BMI. Our cross-sectional models showed a strong correlation between Facebook use and higher BMI. All 3 of these associations dropped out in our prospective models, however, which suggests that those with higher BMI may be more frequent Facebook users, though it is unlikely that Facebook use itself is the cause of higher BMI."
Of the total sample of Gallup survey respondents, a small proportion allowed use of their Facebook data. Those respondents were different from those who did not. They were younger and had more real world friendships. In addition, there were proportionally more women. These are characteristics that are consistent with Facebook users in general . This group is also potentially less concerned with online privacy, as indicated by their allowing access to their Facebook data. How much our results may have changed as a result of these characteristics is hard to say.
"Although we controlled for age and sex in our analyses, we did not control for privacy concerns, so we cannot assess whether this unmeasured characteristic may have confounded our results. However, because participants in this sample had more friends overall, it may have led to an underestimation of our associations, because the positive association of more real-world friendships may have ameliorated the associations of Facebook usage", the report said.