I was going to make this the fourth post on the Facebook/mortality study (“Online Social Integration is Associated with Reduced Mortality Risk“) but am instead making it the third. (See Part One, Part Two, and Interlude.) After this, I will look at the relation (according to the study) between Facebook activities and specific causes of death.
I question the implications of the patterns in the two graphs of Figure 1. The first graph illustrates the association between Facebook friend requests and relative mortality risk; the other, between Facebook friend acceptances and relative mortality risk.
There’s a slight similarity between the two graphs. They both dip downward, hover a little in the middle, dip down some more, and then dip a little upward again. This is no coincidence; the authors acknowledge that they estimated the two friendship categories separately “due to high collinearity between them.”
The first graph (of friend requests) seems to show no significant relation between the activity and mortality risk; the other (of friend acceptances), a possible relation. But Facebook friend acceptances are fewer than requests, almost by definition. (Not all request get accepted, and one can only accept a request that has been made.) Couldn’t this magnify their effects? In any case, I see a lot in common between the two figures; the main difference is in the range of y-values.
But what is going on here, anyway? Both figures show relative mortality risk in relation to the reference category (the mean for each activity, I presume). The second figure has the wider range (between 1.383 and 0.852 times the reference category); to determine whether the differences have meaning, we would need to see the original numbers. In terms of visual effect, the range looks dramatic; in terms of actual numbers, it may be tiny.
I was hoping to get to the bottom of the Cox proportional hazards model, from which these figures are derived; but even the appendix doesn’t reveal the initial numbers or the specific application of the model. The numbers in the two graphs are “adjusted for age, gender, device use, and length of time on Facebook.” Just how does this work? I don’t know, but the adjustments seem somewhat arbitrary. An adjustment for education level or income might be more illuminating. (Update: Actually, they did control for “type of device used,” which was supposed to correlate with socioeconomic status. They also tried controlling for “highest education levels listed by friends on Facebook” but found that this did not substantially alter the results.)
There’s no adjustment, apparently, for length of time between activity and death. In the appendix, the authors state: “To be clear: we are testing associations between 1) social media usage over a six month period and 2) mortality over a subsequent 24 month period, with a 6 month gap between these two measurement periods.” So there’s no distinction between people who were already ill, people who became ill after that period of Facebook usage, and people who died suddenly, with no intervening illness.
Given the “high collinearity” between the two activities and their relation to mortality risk, I also wonder why there isn’t an adjustment for the presence of the collinear activity. It doesn’t seem quite right to separate the two activities when they are so closely related. I suspect that the apparent difference between them is deceptive.
Why does this matter? I take this time with the study because I see in it a combination of good intentions and profound nonsense. Facebook activity isn’t necessarily meaningful or positive; it has a good deal of banality and meanness. Is this the right place to look for insight on the relation between social activity and mortality? Is it the right way? I doubt it. But even if I put aside my initial doubts, I find problems in the logic of the study.
Recently some interesting articles about friendship have appeared; while imperfect, they seem more promising to me than studies of Facebook activity. I will write one more post about the Facebook/mortality study and then proceed to friendship.
Note: I made minor revisions to the fourth paragraph after posting this piece.