In this
[
study](http://www.plosone.org/article/info:doi%2F10.1371%2Fjournal.pone.003…:
Abstract: We test the effects of informal rewards in
online peer
production. Using a randomized, experimental design, we assigned
editing
awards or “barnstars” to a subset of the 1% most productive Wikipedia
contributors. Comparison with the control group shows that receiving a
barnstar increases productivity by 60% and makes contributors six times
more likely to receive additional barnstars from other community
members, revealing that informal rewards significantly impact individual
effort.
I wonder why it is limited to the top 1%? I'd love to see the analysis
repeated (should be trivial) on each decile. Besides satisfying my
curiosity, some rationale and/or discussion of other deciles would also
address any methodological concern about data dredging.