He knows a good deal about the payment rate, too. When he first went into business, he expected 95 percent payment, based on the experience at his own office. But just as crime tends to be low on a street where a police car is parked, the 95 percent rate was artificially high: Paul F.'s presence had deterred theft. Not only that, but those bagel eaters knew the provider and had feelings (presumably good ones) about him. A broad swath of psychological and economic research has argued that people will pay different amounts for the same item depending on who is providing it. The economist Richard Thaler, in his 1985 ''Beer on the Beach'' study, showed that a thirsty sunbather would pay $2.65 for a beer delivered from a resort hotel but only $1.50 for the same beer if it came from a shabby grocery store.

In the real world, Paul F. learned to settle for less than 95 percent. Now he considers companies ''honest'' if the payment is 90 percent or more. ''Averages between 80 percent and 90 percent are annoying but tolerable,'' he says. ''Below 80 percent, we really have to grit our teeth to continue.''

In recent years, he has seen two remarkable trends in overall payment rates. The first was a long, slow decline that began in 1992. ''All my friends say: 'Aha! Clinton!''' Paul F. says. ''Although I must say that most of my friends are conservative and inclined to see such things where others might not.'' The second trend revealed in Paul F.'s data was even starker. Entering the summer of 2001, the overall payment rate had slipped to about 87 percent. Immediately after Sept. 11, the rate spiked a full 2 percent and hasn't slipped much since. (If a 2 percent gain in payment doesn't sound like much, think of it this way: the nonpayment rate fell from 13 percent to 11 percent, which amounts to a 15 percent decline in theft.) Because many of Paul F.'s customers are affiliated with national security, there may be a patriotic element to this 9/11 effect. Or it may represent a more general surge in empathy. Whatever the reason, Paul F. was grateful for the boost. He expends a great deal of energy hectoring his low-paying customers, often in the form of a typewritten note. ''The cost of bagels has gone up dramatically since the beginning of the year,'' reads one. ''Unfortunately, the number of bagels and doughnuts that disappear without being paid for has also gone up. Don't let that continue. I don't imagine that you would teach your children to cheat, so why do it yourselves?''

He is impatient and cantankerous but in sum agreeable. Dressed in jeans and sneakers, with busy eyes and a wavy fringe of gray hair, he awoke this Friday at 3 a.m. Working out of his garage, he first loaded 50 cardboard trays of doughnuts -- a local bakery delivered them overnight -- into the back of his van. He drives an unmarked white Ford E-150 rigged with a bagel-warming compartment. (The van was never stopped during the D.C. sniper attacks, but Paul F.'s tendency to park at the curb caused problems in the near aftermath of 9/11. One customer left a note saying: ''Please park in a parking space. You are freaking a lot of people out.'')

After the doughnuts, Paul F. loaded two dozen money boxes, which he made himself out of plywood. A money slot is cut into the top. When he started out, he left behind an open basket for the cash, but too often the money vanished. Then he tried a coffee can with a slot in its plastic lid, which also proved too tempting. The wooden box has worked well. Each year he drops off about 7,000 boxes and loses, on average, just one to theft. This is an intriguing statistic: the same people who routinely steal more than 10 percent of his bagels almost never stoop to stealing his money box -- a tribute to the nuanced social calculus of theft. From Paul F.'s perspective, an office worker who eats a bagel without paying is committing a crime; the office worker apparently doesn't think so. This distinction probably has less to do with the admittedly small amount of money involved than with the context of the ''crime.'' (The same office worker who fails to pay for his bagel might also help himself to a long slurp of soda while he's filling a glass in a self-serve restaurant, but it is extremely unlikely that he will leave the restaurant without paying.)

After retrieving his hearing aids, he heads for the bagel shop that provides him with roughly 50 dozen bagels, in six flavors, every day. He drives nearly 80 m.p.h. along empty highways and discusses what he has learned about honesty. He is leery of disparaging individual companies or even most industries, for fear it will hurt his business. But he will say that telecom companies have robbed him blind, and another bagel-delivery man found that law firms aren't worth the trouble. He also says he believes that employees further up the corporate ladder cheat more than those down below. He reached this conclusion in part after delivering for years to one company spread out over three floors -- an executive floor on top and two lower floors with sales, service and administrative employees. Maybe, he says, the executives stole bagels out of a sense of entitlement. (Or maybe cheating is how they got to be executives.) His biggest surprise? ''I had idly assumed that in places where security clearance was required for an individual to have a job, the employees would be more honest than elsewhere. That hasn't turned out to be true.''

Since he started delivering bagels, Paul F. has kept rigorous data -- which, when run through a computer and measured against external factors ranging from the local weather to the unemployment rate, can tell some interesting stories. Other conclusions, meanwhile, are purely intuitive, based on Paul F.'s 20-year exposure to bagel behavior.