 The substitutes-vs-complements issue has also been investigated in observational studies. That contributions are perfect substitutes, i.e., that government contributions or other private contributions crowd out an individual’s contribution completely is widely rejected. “Complete crowding out” here would mean that every dollar spent on a public good by the government reduces private spending by the same amount. Most studies find either no crowding out, or a merely a small amount. For example, Kingma 1989 and Kingma &amp; McClelland 1995, focusing on public radio, found only a limited amount of crowding out between 12% and 19% of government expenditures on public radio (i.e., one dollar spent by government reduces private contributions by 12–19 cents).