The United States Postal Service does not get many positive headlines. Facing a $14.1 billion loss this fiscal year, it recently defaulted on a $5.5 billion payment on retiree benefits.

But, at the end of the day, it turns out that they're really good at the one thing that they are supposed to do: Getting letters to their final destination. Economists Alberto Chong, Rafael La Porta, Florencio Lopez-de-Silanes and Andrei Shleifer mailed 1,590 letters to non-existent addresses in 159 countries (10 per country).

They found, in a new working paper, that the United States was, hands down, the fastest to return those letters back to the errant sender. They sent letters back in, on average, 16.24 days. The next closest country - El Salvador - took a full 39 days to return the letter to sender.

Here's the full chart of the 10 countries that returned all 10 letters to the economists (the vast majority of the countries never returned the economists' mail).

The whole point of this study wasn't to test the USPS's robustness, but rather to measure government efficiency and better understand the factors that make a country's day-to-day operations run smoothly.

Management seems to be important. At the end of the day, after all, the whole operation of returning letters to senders rests on managers ensuring that lower-level employees actually "do their jobs [and] putting the incorrectly addressed letter into a correct (return) container, rather than throw it out or get rid of it in some other way."

Technology is the other crucial variable. Countries that have more advanced post-code databases, including street names rather than just cities, were significantly more likely to return an errant letter within three months. In a database that doesn't include street names, the economists point out, "the envelope-reading machine would not detect the wrong address at all, and a person is needed to do it."

Then, there's also your alphabet of choice. Use  of the Latin alphabet significantly increased the odds of a letter winding its way back to these senders by 12 percent. Probably not enough of a boon to encourage countries to change their native language, but one element that does help a letter get where it's going a bit faster.