The study, to be published in June in The New York University Law Review, bristles with data. Its authors coded and analyzed the provisions of 729 constitutions adopted by 188 countries from 1946 to 2006, and they considered 237 variables regarding various rights and ways to enforce them.

“Among the world’s democracies,” Professors Law and Versteeg concluded, “constitutional similarity to the United States has clearly gone into free fall. Over the 1960s and 1970s, democratic constitutions as a whole became more similar to the U.S. Constitution, only to reverse course in the 1980s and 1990s…

There are lots of possible reasons. Our Constitution is terse and old, and it guarantees relatively few rights. The commitment of some members of the Supreme Court to interpreting the Constitution according to its original meaning in the 18th century may send the signal that it is of little current use to, say, a new African nation. And the Constitution’s waning influence may be part of a general decline in American power and prestige.

In an interview, Professor Law identified a central reason for the trend: the availability of newer, sexier and more powerful operating systems in the constitutional marketplace. “Nobody wants to copy Windows 3.1,” he said.