Aug 27, 2021

Exploit Explained: Left-Digit Bias

{This post is part of the Archive of Human Exploits}

“Humans are hardwired to focus on the left digit in numbers. It’s why products are priced at $3.99 instead of $4.00. But does this left-digit bias also affect medical decisions?” asked Dr. Babu Jena in a recent episode of the Freakonomics, M.D. podcast.

Dr. Jena was talking about something called left-digit bias and a study that examined the frequency of surgeries performed on heart-attack patients who were admitted to hospital two weeks before their 80th birthday (while they were still 79) compared to patients who were admitted two weeks after their 80th birthday. Per Forbes, the study found that:

“[P]atients who just turned 80 were 24% less likely to receive cardiac bypass surgery compared to medically similar 79-year old patients who were two weeks shy of their 80th birthday. The 80-year old patients also experienced higher death rates compared to the 79-year old patients, after 30 days of hospitalization.

“Furthermore, these discrepancies were not seen when comparing patients two weeks before and after their 77th, 78th, 79th, 81st, 82nd, or 83rd birthdates. Only the transition from age 79 to age 80 resulted in a statistically significant change in treatment.”

This human exploit has long been known to practitioners is my industry (As Seen on TV), the offer shown at the top of this post being so common it isn't even given much thought anymore. That is, no ASOTV marketer would ever market a product for $15 or $20. It's always $14.99 and $19.99. (On a side note, some still use $14.95 and $19.95 despite the fact this gives away four cents for no good reason. There is no corresponding right-digit bias!) 

We use this little trick because we have long known that prices ending in 99 somehow feel like one dollar cheaper instead of just one penny cheaper. Now, apparently, there's an official name for it.