A natural experiment may be occurring in Santa Barbara. The City Council approved an all vote by mail election for the council election (to save money), which pits three conservative councillors against seven challengers.
The ballot envelopes are postage paid which should increase turnout. County officials are hoping for an increase in turnout from 2009, which they report was “nearly half of registered voters.”
The city clerk’s elections website is here but it’s not clear if ballot envelopes included postage in 2009 (hence no change in 2011).