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Figure: left-digit bias, geriatricsFigureFigureOne of us recently became acutely aware of left-digit bias. It seemed benign at first—a few letters and a freebie from AARP. But then the discriminatory communications began to roll in: “Schedule your screening colonoscopy! Check your lipid panel! Time for the shingles vaccine! Is the PSA for you?” Suddenly, in the course of a single day, a healthy, middle-aged man had transformed into an at-risk senior. But what had actually changed? A left digit had rolled forward. Never heard of implicit left-digit bias? We are here to tell you that it is real, and you and your patients could be at risk. The Evidence Left-digit bias has nothing at all to do with handedness. This bias is one with which we are all familiar, whether we realize it or not. It is the tendency to categorize continuous variables based on the left-most digit. Our minds trick us into thinking items costing $79.99 are a better deal than those costing $80 because seven is obviously cheaper than eight. This bias can also be seen in the used car market, which happens to be booming these days. Prices drop significantly more when the odometer clicks from 79,999 miles to 80,000 than when it advances from 79,899 to 79,900. Some sharp analysts crunched numbers from more than 22 million used car transactions. (American Economic Review. 2012;102[5]:2206; https://bityl.co/CmrS.) Who knew people did this type of number-crunching for a living? They found that cars with odometer readings between 80,000 and 80,100 miles sold for approximately $210 less than cars with odometers that were between 79,900 and 79,999 miles. The drop in price was only $10 when the odometer moved from a similarly sized increase (from 79,800-79,899 to 79,900-79,999) but didn't change the critical left digit. Left digits drive prices, and we intuitively know that. What we may not recognize is that they also influence medical decisions. Left Doesn't Get It Right Consider a recently published study that evaluated the rate of coronary artery bypass grafting (CABG) in patients hospitalized with acute myocardial infraction. (N Engl J Med. 2020;382[8]:778; https://bityl.co/CmrT.) Knowing CABG is a high-risk procedure, cardiologists and surgeons might think it less suitable for older patients. But which birthday counts as being older? These investigators thought 80 would be a decision-making threshold, even though this age is not specified in the guidelines. The study compared CABG rates between those who had just celebrated their 80th birthday (less than two weeks) with those whose 80th birthday was just around the corner (less than two weeks). The two groups were virtually the same age and were identical in baseline characteristics. You can probably guess what the investigators found. The older patients (perceived as being in their 80s) were less likely to receive CABG than their younger counterparts (perceived as being in their 70s), even though the age gap (less than four weeks) was negligible: 5.3 percent (265 of 5036 patients) v. seven percent (308 of 4426 patients), p<0.001. Were there similar differences in CABG rates bordering other birthdays, like the 77th, 78th, 79th, 81st, 82nd, or 83rd? None at all. That left digit makes a considerable difference. And the evidence that left doesn't get it right doesn't stop there. The probability of a donor organ being placed dropped by 5.4 percent from donor age 69 to 70 in a large cohort (105,387) of potential donors between 2010 and 2019. (Am J Surg. 2022;S0002-9610[22]00217-3.) Left-digit bias has not been well studied in ED practice, but one can imagine how our patients before and after a decade-altering birthday might be affected. Might you be more likely to have a goals-of-care conversation or make a palliative-care referral with a 90-year-old versus an 89-year-old? Or be less aggressive in your ED diagnostic workup? Or order insufficient analgesia? Or have a surgeon recommend conservative versus aggressive management? The Verdict A popular trend using this bias can be found in the wellness community by those who peddle and profit from selling an assessment of “biologic” age. In fact, it is quite easy to find online calculators that will figure this out for you. A quick search landed us here: https://bit.ly/39EtSzS. These seem to be back-of-the-envelope calculations based on some broad epidemiological evidence (smoking and obesity decrease life expectancy), but they do have some face validity. We know intuitively that some of our patients will be “old” 60-year-olds and others will be “young” 70-year-olds. Maybe our ED demographics should have two ages entered: chronological and biologic. This may help us temper any implicit left-digit bias. The one of us who was a recent victim of this insidious left digitness took solace in the fact that the good people at Easy Calculation considered his biologic age on the right side (that is, younger side) of 50. Looks like there will be an opportunity to plan another big birthday party. Share this article on Twitter and Facebook. Access the links in EMN by reading this on our website: www.EM-News.com. Comments? Write to us at [email protected]. Dr. Vinsonis an emergency physician at Kaiser Permanente Sacramento Medical Center, a chair of the KP CREST (Clinical Research on Emergency Services and Treatment) Network, and an adjunct investigator at the Kaiser Permanente Division of Research (https://www.kpcrest.net/). Dr. Ballardis an emergency physician at San Rafael Kaiser, a past chair of the KP CREST Network, and the medical director for Marin County Emergency Medical Services. Follow him on Twitter@dballard30. Read their past articles athttp://bit.ly/EMN-MedClear.
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