While hand-drawn, the sources for the data were given:
http://www.sciencedirect.com/science/art...9608000238
http://www.sciencedirect.com/science/art...9606001061
http://psycnet.apa.org/psycinfo/2011-16524-001/
http://www.sciencedirect.com/science/art...9608000238
http://www.sciencedirect.com/science/art...9606001061
http://psycnet.apa.org/psycinfo/2011-16524-001/