Often economics is about finding the right chart to express a certain phenomena. Take a look at the 3 distinct periods above:
- Before 1999 and the creation of the Euro: Yields on the Greek, Spanish, Italian and Portuguese are much higher than the ones of France and Germany.
- From 1999 to 2008: Yields of all Euro countries converge dramatically. To get a sense of the reason for this, read the first paragraph of Part 3 of my note on the Euro Crisis.
- From 2008 and the onset of the crisis onward: Yields diverge dramatically again, but this time with the same currency across all Euro countries!
I find this to be quite a good illustration of what was happening.