There are many trends that you can track with people and how they respond to different situations. Anyone who’s planned an event has probably realized that the majority of people RSVP in the last time frame, which can make predicting expected numbers of registrants difficult.
A recent paper in Nature Physics examines data from several recent physics conferences and determines the rate at which people register. The data initially begins linear, but spikes logarithmically near the deadline. They summarize that you can predict the total number of registrants by extrapolating the linear registration data to the deadline and tripling that number.
Valentina Alfi, Giorgio Parisi & Luciano Pietronero
Nature Physics 3, 746 (2007)
If you don’t have access to this journal you can still view the graph (the article is only a page so you get most of the info from the graph).