Below is a nice little graphic that I generated from an exploration tool provided by the good folks at the Organisation for Economic Cooperation and Developement. It shows the relationship of population distribution and GDP per head. Each point is a country. The axes are % of population below 14 and above 50. So countries in the top left endure the terrible aging armageddon that Australia is supposedly heading for (lots of old people and few young people). Bottom right countries are (dynamic?) youthful countries. The GDP per head is measured by the size of the blobs.
But hold on. According to this graphic, higher GDP countries tend to have a higher proportion of elderly and a lower proportion of young people. Hell, those old folks must be productive and smart!. Our aging population is a great thing!? I might use this one as a nice causation example in class. Not to mention showing how to display three or four dimensions in a graphic.
P.S. I which I could recall what the colour represented. I generated this graphic several months ago and left this post sitting in draft.
P.P.S Anyone know of an R or Excel tool that produces nice four dimensional graphs? Using size, and especially colour, can be a bit tricky because visual impressions of size and colour trends do not necessary follow the natural numerical measures.