We mailed letters to non-existent business addresses in 159 countries (10 per country), and measured whether they come back to the return address in the US and how long it takes. About 60% of the letters were returned, taking over 6 months, on average. The results provide new objective indicators of government efficiency across countries, based on a simple and universal service, and allow us to shed light on its determinants. The evidence suggests that both technology and management quality influence the quality of government.The authors explain:
All countries subscribe to an international postal convention requiring them to return the letters posted to an incorrect address. We measured the fraction of letters that were actually returned, and how long it took the letters to come back from the date they were posted from Cambridge, MA. We stopped keeping track of returns one year after the final postings that took place on Feb 4, 2011. We do not believe this procedure aroused any concerns or delays at the US post offices. We use the data to construct the share of letters we got back, and how long it took to get them back, in each of 159 countries, and then to analyze a variety of correlates of these measures of postal efficiency.Source.
Top and bottom countries (El Salvador is top 2):