Here is a helpful chart that gives this data: http://econlog.econlib.org/archives/2015/03/the_prevalence_1.html http://econlog.econlib.org/archives/2015/03/the

Here is a helpful chart that gives this data: http://econlog.econlib.org/archives/2015/03/the_prevalence_1.html http://econlog.econlib.org/archives/2015/03/the_prevalence_1...