Americans are disgusting. Actually, let me rephrase that: 45% of Americans are disgusting. According to a study, 45% of them have worn the same pair of underpants for two days or longer. The survey also found that men are almost 2.5 times more likely than women to wear their underwear for more than a week.

Before you get too grossed out, let me stress that this study should be taken with several pinches of salt. This was not a rigorous scientific investigation published in the Journal of Hygiene; it was a survey conducted by an underwear company to generate free coverage and encourage you to buy new underwear every six months. The company does not reveal how its questions were phrased and is vague about methodology; it does not specify, for example, whether the 2,000 Americans polled were a representative sample or were just college students. In brief, the results stink to high heaven. Nevertheless, the survey went viral and was reported by outlets such as Newsweek, the Independent and the New York Post.

Running a study to come up with a headline-worthy statistic you can use to flog your product is PR 101. I can tell you from my own experience in the ad industry that agencies are full of people desperately designing surveys and cutting data until they generate a juicy statistic for a client. I call these types of stats “advertistics” and I suggest you do too – like 72.5% of writers, my greatest ambition is to one day appear as the source for a word in the OED. With enough patience, you can get a survey to prove anything, no matter how ludicrous. A genetics company, for example, can “prove” that genes determine whether you love or hate Marmite; the US National Dairy Council can claim that 7% of American adults think chocolate milk comes from brown cows.

Advertistics are largely harmless fun, intended simply to insert a brand name into a cultural conversation. It’s when you do not see a brand attached to a dubious-sounding statistic that alarm bells should start ringing. You may remember headlines earlier this year claiming that half of Americans admit they use swimming pools to wash instead of the shower. The survey turned out to have been by a PR firm working for the chlorine industry – something a number of news outlets did not initially notice or report.

In general, brand-sponsored studies generate a few headlines and are swiftly forgotten. Sometimes, however, they become received wisdom. Take, for example, the idea that breakfast is the most important meal of the day – something your mum probably yelled at you multiple times when you were a kid. You can largely thank Edward Bernays, who is considered the “father of public relations”, for drumming this idea into our psyche. In the 1920s, Bernays (who was Sigmund Freud’s nephew) was hired by the bacon industry to increase sales. He did so by surveying 5,000 doctors and asking them if “a hearty breakfast was better than a light breakfast to replace the energy lost by the body at night”. A majority of doctors agreed and the survey results became the cornerstone of an ad campaign encouraging you to start your day with a hearty breakfast of bacon and eggs.

This, by the way, is not to say that all statistics are complete bunk. A study conducted by Arwa Mahdawi LLC has found that the small percentage of people who read until the very end of an article are extremely intelligent, very attractive and definitely change their underwear every day. Well done, you.

• Arwa Mahdawi is a Guardian columnist