BOSTON — It’s easy to see why iPods would be alluring targets for criminals: The music players are valuable and easy to resell. But could the temptation for stealing iPods be so strong that they’re behind an increase in the crime rate?

Researchers at the Urban Institute, a Washington think tank, say yes.

They argue that the tantalizing gadgets are perhaps the main reason U.S. violent crime rose in 2005 and 2006 after declining every year since 1991, although a look at the findings suggests the hypothesis has holes.

A key point in the Urban Institute’s argument is that robberies had seen dramatic reductions since the 1990s, but jumped in 2005 and 2006. During those years, iPods were going mainstream. In late 2004, Apple had sold about 5 million iPods. By the end of 2005 that had ballooned to 42 million, and in 2006 the number neared 90 million.

Anecdotal evidence bears out a lot of this. Subway officials in New York, San Francisco and Washington, D.C., reported big increases in iPods being stolen from passengers. People listening through the iconic white earphones are easy to pick out and often unaware of their surroundings.

Furthering this idea, the rate for robberies by juveniles increased during this “iCrime Wave” to a much greater degree than the rate for adults, Urban Institute researcher John Roman pointed out.

It’s curious that while iPod thefts on subways and other crowded urban settings provide the best anecdotal evidence, the 2005-06 crime increases were highest in small and midsize cities — places with less-dense pedestrian traffic, let alone teeming subways.

Also, some stolen iPods might fall into the category of larceny — a theft without force, such as when something is filched from a backpack — and larcenies dropped in ‘05 and ‘06.

In other words, there might have been an iCrime wave, but it would be hard to be sure. Robberies also jumped in pre-iPod 2001.

“I guess I could sort of understand and buy that in a very narrow place, in a short period of time — a short spike for a few months,” said Jack McDevitt, associate dean at Northeastern University’s College of Criminal Justice. “But to suggest that that’s driving the crime numbers in any major way, I don’t think so.”