Why do people give? Is giving a purely altruistic act, or is some utility received when those we give to receive utility as a result of our actions? A particularly salient question is whether so-called social effects, or group size effects, can be explained by such a “warm glow” motive. That is, does an individual propensity to give or contribute to a public good depend on the number of people who will be helped by, or will consume, that public good?
Zhang and Zhu consider an interesting natural experiment. Beginning in late 2005, Wikipedia was blocked in mainland China for over a year. Because all changes to wikipedia pages are saved, if we knew who was posting from China and who was posting from other Chinese-speaking locations (say, Taiwan or Singapore), we could investigate the effect of a massively decreased readership on the willingness to contribute.
The authors identify non-mainland users by checking who uses traditional Chinese script, common in Singapore and China, but not in Taiwan and Hong Kong, and by checking who posted both before and after the block, since presumably mainland users would not be able to post after the block went into effect. After controlling for how long the user had been posting on Wikipedia (since posts are most frequent soon after the first post is made). They identify a decrease in propensity to post of more than 40%.
Robustness checks found a handful of other interesting results. Removing politically sensitive topics does not change the result (so the decrease isn’t simply reflecting fewer back-and-forth battles over whether Taiwan should be listed as part of China). Those who post most on “Talk” pages, where potential revisions of Wiki pages can be discussed, were most likely to decrease their posting; presumably these posters were the ones for whom social effects were most important. Only examining new pages, rather than revisions of old pages, gives similar results.
At this point, I have to bring up the obvious critique that any non-empirical person will have about papers of this kind: external validity. To the extent that we care about social effects, we care about how they will manifest themselves on important social questions – for instance, what will happen to volunteer rates after some public policy change – and not about Wikipedia per se. Without some sort of structural or theoretical model, I have no idea how to apply the results of this paper to other, related questions. Even lab experiments, of which I’m also skeptical, provide some sort of gesture toward external validity. Note that this isn’t my critique by any stretch: the “why do we care about sumo wrestling match fixes?” critique has been made by many, many theorists and structural empiricists, and it strikes me as wholly valid.