The paper ranks country corruption according to the number of parking violations per country diplomat, and finds that the results match up remarkably well with findings from rough survey-based estimates on the topic. Who are the worst violators? Kuwait blew away the competition with a whopping average of 246 unpaid parking tickets per diplomat over a 5 year period. Diplomats from countries famed for their good political behavior like Canada, Sweden, and Norway didn't have any unpaid tickets.
Interesting data on who would break the law if they could get away with it. Diplomats are granted immunity from prosecution so therefore can break the law without being punished. This isn't actual true as I imagine most countries that respect the rule of law do not tolerate diplomats that flaunt laws of the countries they visit.
I believe in addition to having ethical diplomats the countries that are behaving well have senior government officials that would not allow such poor behavior from their representatives. Which explains why Foreign Policy magazine found such a correlation between corruption and those diplomats behaving irresponsibly.