BOSTON — It's easy to see why iPods would be alluring targets for criminals: The music players are valuable and easy to re-sell, and people absorbed in their personal soundtracks can be vulnerably oblivious to their surroundings.

But could the temptation for stealing iPods be so strong that they're behind an increase in the crime rate? Researchers at a public policy institute 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 close look at the findings suggests the hypothesis has holes.

The Urban Institute, a Washington think tank, first raised the subject of an "iCrime wave" last September, and held a panel discussion yesterday to explore it further. The researchers don't blame iPod maker Apple Inc. or any other device maker for crime, but they do say consumers should demand technologies that would render stolen gadgets useless.

A key point in the Urban Institute's argument is that robberies — the taking of something by force or the threat of it — had seen dramatic reductions since the 1990s, but jumped in 2005 and 2006. FBI statistics show the robbery rate went from 137 per 100,000 people in 2004 to 141 per 100,000 in 2005 and 149 in 2006. That helped boost the overall rate of violent crime in those years, even as rape rates fell and aggravated assault was generally flat.

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.

One widely accepted theory holds that crime happens when three things come together: A motivated offender encounters a suitable victim and perceives a high chance of getting away with it. And the Urban Institute researchers believe the sudden prevalence of iPods increased all three factors.

Motivation: The iPod's several-hundred-dollar expense and pop-culture buzz made potential thieves, especially young ones, crave the device for themselves or for a lucrative resale market. Suitable victims: People listening through the iconic white earphones are easy to pick out and often unaware of their surroundings. Easy to get away with: IPods lack a mechanism that would pinpoint a thief's location or a subscription that could be canceled by the rightful owner.

But is it plausible that so many iPods and similar gadgets were stolen that they drove the rising robbery rate? That robbers would not have just stolen something else if not for shiny music players? This is where the iCrime Wave begins to seem less certain.

For one thing, homicides also increased in this same span, albeit slightly, from 5.5 per 100,000 people to 5.6 in 2005 and 5.7 in 2007. Since crime trends are often murky, whatever caused the bump in homicides might also explain the rise in robberies.

It's also 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 mid-sized 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 2005 and '06.