SGIM FORUM 2011; 34(11) CHALK TALK Thinking about Thinking: Medical Decision Making Under the Microscope Christiana Iyasere, MD, and Douglas Wright, MD, PhD Drs. Iyasere and Wright are faculty in the Inpatient Clinician Educator Service of the Department of Medicine at Massachusetts General Hospital in Boson, MA. ase: A 36-year-old African-Ameri- athletic—he graduated from college than 10 seconds and says “20,160” C can woman, healthy except for with a degree in physics and has before moving breezily along with treated hypothyroidism, visits you in completed several triathlons. Neil is a her coffee. Having Katrina’s input, are clinic complaining of six months of fa- veteran of the US Navy, where he you tempted to change your answer tigue and progressive shortness of served as fleet naval aviator and land- to questions 3a and 3b? Go ahead, breath with exertion. You thoroughly ing signal officer. Is Neil more likely to admit it. Aren’t you now more confi- interview and examine the patient. be: a) a librarian or b) an astronaut? dent that the correct answer is that Physical examination reveals conjunc- Question 2: Jot down a list of the product is closest to 20,000? tival pallor and dullness to percussion English words that begin with the let- Question 5: You have known one third of the way up both lung ter “r” (e.g. rooster). Next, jot down your medical school roommate Jus- fields. Something tells you to ask her a list of words that have an r in the tice for four years. You trust him ab- about skin rashes, and you learn that third position (e.g. forsake). Is the let- solutely and have confided in him she has had worsening sun sensitiv- ter r more likely to occur at the start many times. Justice is always ity for the past year. A light bulb goes of words or in the third position? smartly dressed, and he loves to on in your mind. Along with routine Question 3a: In no more than 10 shop. You are at a mall shopping with labs and a TSH, you order an antinu- seconds, estimate the product 1 x 2 Justice when you briefly notice him clear antibody test and a chest X-ray. x 3 x 4 x 5 x 6 x 7 x 8 = n, and an- down another aisle putting what You find the hematocrit to be 25%, swer quickly whether n is closer to a) looks like a belt into his knapsack. (In the TSH normal, and the ANA to be 1,000; b) 10,000; c) 20,000; or d) truth you can’t tell whether he was positive at 1:1024. The chest film 50,000. Mark your answer and move putting the belt into the knapsack or shows large bilateral pleural effu- immediately to the next question. taking it out, and if pressed you sions. You make the diagnosis of sys- Question 3b: Now, wipe your couldn’t be 100% certain that it was temic lupus erythematosis. mind’s “slate” clean, and again in a belt. You think nothing of this.) A Elementary, right? But how did no more than 10 seconds, start in few minutes later you are shocked to you arrive at this diagnosis as op- reverse order, and estimate the find two security guards interrogating posed to another? Coming to an ac- product 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 Justice, accusing him of stealing a 1 curate diagnosis is based on pattern = n. Answer quickly whether n is belt. Justice insists that the belt was recognition, algorithmic thinking, and closer to a) 1,000; b) 10,000; c) already in his bag. It seems odd that deductive reasoning—all enriched by 20,000; or d) 50,000. Resist the the belt still has the price tag on it, experience. We rely on these tools to temptation to calculate the exact but you trust Justice, assume that he parse through all the information that answer. is telling the truth, and stand by him is presented to us. Making accurate Question 4: As it happens, your in his argument with the security diagnoses with incomplete and often friend Katrina (a former Russian child guards. Thinking back, you wonder contradictory information in limited chess champion and math whiz) how Justice affords the expensive time is the playing field of the in- passes by the Starbucks lounge chair clothes that he wears, given his ternist. However, the very processes where you sit answering question 3. modest income. Later that month, that help us think are likely to incor- You like Katrina but sometimes tire of despite your appearance as a charac- rectly bias our thinking and cause di- the way she drops hints about her in- ter witness at his trial, Justice is con- agnostic error. In essence, our minds telligence and math prowess. (How, victed of shoplifting and ordered to are sometimes misled not only by the you wonder, did she manage to tell pay a $500 fine and to perform 40 facts themselves but also by how we you that she scored 800 on the math hours of community service. think. The often helpful but some- SAT?) It bugs you that she always Given this new and quite startling times dangerous shortcuts that we says that her undergraduate degree development, will you: take in thinking are called heuristics.1 from Princeton was in “mathemat- To explore the concept of heuris- ics.” (Why can’t she just say “math” a) Believe Justice’s denial of guilt tics, please take the following quiz. like a normal person?) And it is espe- (he is after all your good friend Question 1: Consider Neil, a 44- cially irritating that Katrina now whom you trust) and carry on as year-old man from Santa Monica, Cal- glances at the multiplication you if nothing had happened?; ifornia. He is well educated and have just tried to estimate in less continued on page 2 CHALK TALK continued from page 1 include on our differential some diag- Step running product of: running product of: noses that may be more common 1 x 2 x 3 x 4 x 5 x 6 x 7 x 8 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1 1 256than ones we have thought of but 2 6 336 are less familiar to us. For example, 3 24 1,680 when asked to list causes of 4 120 6,720 petichiae in hospitalized patients, 5 720 20,160 many physicians will include vasculi- 6 5,040 40,320 tis and endocarditis (both of these 7 40,320 40,320 causes are drilled into us during med- ical training) but forget to include b) Begin to reevaluate your one of NASA’s 62 elite astronauts. NSAID-induced platelet dysfunction, relationship with Justice, perhaps Clinical examples of the danger of which is more common. A variant of thinking twice about confiding in the representativeness heuristic the availability heuristic is called last him as you have?; or abound, and we are in daily danger case bias, in which your experience c) Jettison your friendship with of falling prey to it. Indeed, we are with a particularly memorable case Justice? sometimes encouraged to use repre- causes you to overestimate the likeli- sentativeness by the following admo- hood of the condition in subsequent Discussion of Quiz Questions nition: “If it looks like a duck, walks differential diagnoses. For example, if Question 1. The description of Neil like a duck, and quacks like a duck, you recently had a pancytopenic pa- was crafted to vaguely characterize it’s a duck.” However, if a “duck” ap- tient who turned out to have hairy an astronaut—an intelligent, athletic, pears in a part of the world where cell leukemia, which is exceedingly motivated man with a background in this would be unlikely, such as the rare, you might overestimate the like- aviation and physics. If you are like Sahara Desert, perhaps one should lihood that your next pancytopenic many smart people who have an- reconsider the label or rename the patient has hairy cell leukemia, by- swered this question, you therefore creature something more broad, like passing other more common causes chose astronaut and fell victim to “a feathered animal with wings and of pancytopenia. what is referred to as the represen- a bill, resembling a bird.” Awareness Questions 3a and 3b. How did 2 tativeness heuristic.1 In short, you ig- of the danger of representativeness your estimate of the product 1 x 2 x nored prior probability. According to has given rise to the clinical maxim 3 x 4 x 5 x 6 x 7 x 8 compare with the American Library Association “an uncommon presentation of a the same product shown in reverse (www.ala.org), there are approxi- common disease is more common order as 8 x 7 x 6 x 5 x 4 x 3 x 2 x 1? mately 122,000 US libraries, employ- than a common presentation of a If you are like most people, your esti- ing 150,000 librarians. (This does not rare disease.” mate was larger when the product count 190,000 other paid staff who Question 2. We daresay that most was presented in descending order.1 work in libraries.) According to NASA people had a harder time, worse luck, This is because when estimating a (www.jsc.nasa.gov/Bios), there are and scratched their heads more com- product expressed in descending 62 active astronauts.