I just posted an entry in Wikimedia's blog explaining part of a study I'm working on with some Wikimedians (Wikipedians working at the Wikimedia Foundation). In response to speculation that the English Wikipedia's editor decline could be the result of a general decrease in the quality of newcomers to the site, we performed a hand-coded evaluation of the first few edits performed by editors over time.
Overall, we found that the quality of newcomers has not substantially decreased since 2006. While the rate at which these good newcomers have their contributions reverted or deleted has been rising over time, the survival rate of good new editors has been falling. This supports our working hypothesis that the increased rate of rejection for new editors is causally related to the decline in the survival of new editors.
See the full report here: http://meta.wikimedia.org/wiki/Research:Newcomer_quality
This analysis is part of a larger contribution in submission to a special issue of American Behavioral Scientist on Wikis. Stay tuned.
I've recently been hearing a bit about Mark Penn's book "Microtrends: The Small Froces Behind Tomorrow's Big Changes". As this review says, Penn analyzes poll and survey data to identify 75 important microtrends (which appear to correspond to 'small' segments of the US population, say at least 3 million) that, he believes, are interesting and important.