@techreport{sto-09-wikigr-tr,
   author = {Jorge Stolfi},
   title = {A Two-Phase Model for {Wikipedia} Growth},
   month = nov,
   year = 2009,
   number = {IC-09-45},
   institution = {Institute of Computing, State University of Campinas},
   pages = {17},
   abstract = {The number of articles $N(t)$ in Wikipedia is quite accurately modeled as a function of time $t$ by two exponential regimes or phases, with a relatively sharp transition over a one-year period centered on Janary 2006. The first regime has a positive rate constant  $R_1 = +0.00217$ per day, corresponding to a doubling time of about 10.5 months. The second regime has a negative rate constant  $R_2 = -0.000407$ per day, corresponding to a halving time of about 4.5 years. The model predicts that $N(t)$ will tend to a finite limit of about 5.9 million articles. We advance some possible explanations and implications of the negative rate.},
  altkeys = {TR-IC-09-45}
}