I had an essay in the Wall Street Journal on Friday called Overestimating Our Overworking. Here’s the text, below:

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Summer is here again. It heralds the return of barbecues, white pants, barbecue-stained white pants and, for many workers, that perk known as Summer Fridays: half-days that allow everyone to start the weekend early.

Heaven knows we need the time off — or think we do. Over the past two decades of rapid technological deployment and globalization, it has become an article of faith among the professional set that we work sweatshop hours. Sociologist Juliet Schor started the rumor with her 1992 book, “The Overworked American,” which featured horror stories of people checking their watches to know what day it was.

Then God created the BlackBerry and things got worse. In late 2005, Fortune’s Jody Miller claimed that “the 60-hour weeks once thought to be the path to glory are now practically considered part-time.” In late 2006, the Harvard Business Review followed up with an article on “the dangerous allure of the 70-hour workweek,” calling jobs that required such labor the new standard for professionals. The authors featured one “Sudhir,” a financial analyst who claimed to work 90-hour weeks during summertime, his “light” season. He’s got nothing on a young man I met at a party recently who told me he was working 190 hours a week to launch his new company.

It was a curious declaration; I would certainly invest in a start-up that had invented a way to augment the 168 hours that a week actually contains. The young man turned out to be kidding. But he felt overworked, and so he indulged in some workweek inflation. Research shows that this is a common affliction among anyone claiming to work more than 50 hours a week. Indeed, almost no one claiming to work 70-, 80- or 190-hour weeks is actually doing so. This doesn’t make Summer Fridays any less sweet. But it does raise the question of why our perceptions of work are so different from the reality.

Sociologists have been studying how Americans spend their time for decades. One camp favors a simple approach: if you want to know how many hours someone works, sleeps or vacuums, you ask him. Another camp sees a flaw in this method: People lie. We may not do so maliciously, but it’s tough to remember our exact workweek or average time spent dishwashing, and in the absence of concrete memories, we’re prone to lie in ways that don’t disappear into the randomness of thousands of answers. They actually skew results.

That’s the theory behind the American Time Use Survey, conducted annually by the Bureau of Labor Statistics. The ATUS, like a handful of previous academic surveys, is a “time diary” study. For these studies, researchers either walk respondents through the previous day, asking them what they did next and reminding them of the realities of time and physics, or in some cases giving them a diary to record the next day or week.

Time-diary studies are laborious, but in general they are more accurate. Aggregated, they paint a different picture of life than the quick-response surveys featured in the bulk of America’s press releases. For instance, the National Sleep Foundation claims that Americans sleep 6.7 hours (weekdays) to 7.1 hours (weekends) per night. The ATUS puts the average at 8.6 hours. The first number suggests rampant sleep deprivation. The latter? Happy campers.

The numbers are equally striking with work. Back in the 1990s, using 1985 data, researchers John Robinson and his colleagues compared people’s estimated workweeks with time-diary hours. They found that, on average, people claiming to work 40 to 44 hours per week were working 36.2 hours — not far off. But then, as estimated work hours rose, reality and perception diverged more sharply. You can guess in which direction. Those claiming to work 60- to 64-hour weeks actually averaged 44.2 hours. Those claiming 65- to 74-hour workweeks logged 52.8 hours, and those claiming workweeks of 75 hours or more worked, on average, 54.9 hours. I contacted Prof. Robinson recently to ask for an update. His 2006-07 comparisons were tighter — but, still, people claiming to work 60 to 69 hours per week clocked, on average, 52.6 hours, while those claiming 70-, 80-hour or greater weeks logged 58.8. As Mr. Robinson and co-author Geoffrey Godbey wrote in their 1997 book “Time for Life,” “only rare individuals put in more than a 55-60 hour workweek.”

I thought I was one of them. So I kept a time diary. Alas, even during a week that left me feeling wrecked, an honest accounting of my hours didn’t top 50.

There are many reasons for such discrepancies. The first is the gray definition of much white-collar labor. If you’re watching “Talladega Nights” on a flight to a conference, are you working? Is reading the Taste page of The Wall Street Journal in your office work? Anyone claiming an 80-hour workweek is definitely putting both in the “yes” category — though this mode of calculation is going to result in more generous estimates than an observer might tally.

The second reason people overestimate is that they discount exceptions that don’t fit the mental pictures they create of themselves. If you work four 14-hour days, then quit after 8 hours on Fridays, you’d think a “usual” day was 14 hours, meaning that you work 70-hour weeks. But you don’t. You work 64 — maybe. You probably work less than 14 hours on holidays such as Memorial Day. Plus, odds are good that your 14-hour days feature some late arrivals, lunch breaks or phone calls to your spouse. Pretty soon we’re back below 60. You might have worked on weekends. But here we tend to overestimate time devoted to small, repetitive tasks. People think they spend far more time washing dishes than they do. Likewise, if you pulled out your BlackBerry 10 times over the weekend, you might give yourself credit for several hours of work, even though each incidence took five minutes. Total time? Less than one hour, even though you feel as if you’re in work mode 24/7.

Finally — and this is the big one — work is a competitive sport. In an era with little job security, we all want to seem busy and hard-working. If publications such as Fortune call 60 hours “part-time,” what professional would claim to work less?

Of course, even if we work fewer hours than we think we do, perceptions matter. Taking numerous breaks during the day so you have the stamina to stay until 8 p.m. is more draining than going home at 6. Even if your BlackBerry isn’t buzzing at 10 p.m., the fact that it might is a source of stress. So maybe we can all take a little time to relax this summer and enjoy our Summer Fridays, instead of complaining to our friends about how overworked we are.

Ms. Vanderkam is writing a book, “168 Hours,” to be published by Portfolio in 2010