Word of the attempted assassination of Representative Gabrielle Giffords outside a Tucson supermarket, which left her in critical condition after a bullet passed through her brain, had barely broken before speculation erupted on the motivations of the man accused of shooting her and killing six others, Jared Lee Loughner, 22.

Was Mr. Loughner a conservative or a liberal? What did he think of the Tea Party? How serious was his degree of mental illness? What role, if any, did heated political rhetoric and violent political metaphors play in his decision to shoot the congresswoman and 19 other people who were at the scene, including a federal judge?

The search for answers is understandable — although, with this being the first tragedy of quite this kind in the Twitter Age, I have been a little surprised at the velocity at which it has taken place. Increasingly, thanks to the outstanding reporting by The Times and other news organizations, we’re gaining more insight into Mr. Loughner and his state of mind. Still, there is much more to learn about the case, and even when the preponderance of evidence is in, it is likely that we will never understand exactly why he chose to do what he did.

Suppose, however, that our focus is on something slightly different: on estimating the risk posed by assassinations of public officials in the future, and thereby doing our best to prevent them. Here, there is probably the risk of overgeneralizing the lessons learned from just one attack, however terrible it was.

Assassinations are remarkably rare in America. The last sitting member of Congress to have been assassinated was Representative Leo J. Ryan of California, who was murdered by members of the People’s Temple when he was visiting Guyana in 1978. The last one to be assassinated on American soil was Senator Robert F. Kennedy of New York in 1968.

The last mayor of a large city to be assassinated was George Moscone of San Francisco, who was killed along with a city supervisor, Harvey Milk, in 1978. The last American president to be assassinated was John F. Kennedy in 1963, although there have been attempts or very serious threats against several others since, most notably Ronald Reagan, who was shot but not killed by John Hinckley, Jr., in 1981. Gov. George Wallace of Alabama was shot and left partly paralyzed by a would-be assassin while running for president in 1972.

As James Fallows has noted, it is hard to come to any blanket conclusions about assassins and their motivations. Some of them seem to have made an explicitly political calculation, while some were completely detached from reality. Many had obscure grievances that did not match the mainstream political debates of their day.

These assassinations and assassination attempts, including the one against Ms. Giffords, cannot be thought of as “random” incidents. By definition, an assassination requires that a specific public official be the target for murder, and the authorities say Mr. Loughner seems explicitly to have targeted Ms. Giffords.

They have, however, been isolated incidents in several different senses of the term: because of their rarity; because there is little to link them together; and because virtually all were the acts of lone individuals, and not part of larger conspiracies.

That makes them, for someone concerned with estimating the risk of similar future attacks and preventing them, exceptionally difficult to study. It is almost impossible to come to meaningful conclusions about probability from a sample size of one.

Mr. Loughner’s case so far seems to be no exception. Apart from his somewhat inscrutable state of mind, other facts and circumstances of the case are also unusual, such as the fact that he shot at least 19 others in addition to Ms. Giffords, something which is uncommon in an assassination attempt.

Even if Mr. Loughner’s profile were a little clearer, however, there would still be the risk of overgeneralizing from any one case. The next would-be assassin might be very much like him, or he might not.

What we do have in some abundance, however, are threats of violence: these are fairly common. For instance, there were 49 credible threats recorded against United States senators in 2010, according to the office of the Sergeant at Arms.

Many of these, undoubtedly, were made by people who had no real intention of carrying though with attacks. Still, it seems reasonable to hypothesize that they might stem from some of the impulses that an actual attack might, and might be of some value in our efforts to anticipate them.

The number of threats against members of Congress seemed to have been on the decline throughout most of the past decade. There is some evidence, however, that their number has increased significantly in the past year or two. The Sergent at Arms, for instance, counted just 29 threats against senators in 2009, rather than 49 in 2010. And there was a 300 percent increase in such threats against all members of Congress (both representatives and senators) in the first few months of 2010, according to the same office.

The journalist Ronald Kessler, meanwhile, wrote in his bestselling book that there has been a 400 percent increase in the number of threats against the White House since Barack Obama took office.

These sorts of statistics are a bit frightening. But they do, for better or for worse, provide us with a reasonably robust data set. If it turns out, for instance, that Democratic members of Congress are much more likely to receive such threats than Republican ones, that might tell us something meaningful. Likewise, if threats made against Mr. Obama routinely invoke his race, that could tell us something too.

It might also be possible, with careful study, to see whether there is a correlation between the frequency of different types of political rhetoric and the number of such threats. Searches of Lexis-Nexis, for instance, could determine whether violent political metaphors have in fact become more common, and if so, whether their timing coincides with with them.

I don’t know whether such data could be entirely “open source,” considering its sensitivity. But perhaps the Sergent at Arms, and other parts of the security apparatus, could make a few such statistics available to the public on a regular basis. It would probably provide us with considerably more insight into the risks posed by assassination, domestic terrorism, and other severe forms of political violence, than any degree of scrutiny of Mr. Loughner’s case could on its own.