Omission Bias in Therapeutic Medical Decision Making

Having studied so-called heuristics and biases, aka cognitive biases and System 1 & System 2 processes in medical decision making on and off for 25 years, and thinking constantly about them in the full-time practice of clinical medicine, I have come to the conclusion that they are hard to spot in the wild. Except one: Omission Bias.

Omission bias represents a preference for inaction that preserves the status quo over action which changes it, and it is insidious because each day we encounter countless status quo states in medicine, established earlier and perhaps by different providers, but often by ourselves. The status quo inures us to what is, obscuring the question of what ought to be.

In this recent paper, and an accompanying editorial, omission bias is (partly) explained and several recurring examples in the ICU are discussed. But this is the tip of the iceberg. I venture a guess that every day, there is a decision that is made, or not made, that instantiates this bias. In addition to those discussed in the linked papers, here I will point out some common scenarios outside of the ICU where this bias lurks, preying on the desultory physician.

The patient presented to the ER (or elsewhere) for pneumonia, and was started on Zosyn (or cefepime) and vancomycin. Despite having no risk factors for pseudomonas, anaerobes, or MRSA, the team continues those antibiotics rather than change them to standard CAP coverage. The prospect of not covering something, always nagging at the physician, now looms larger because if the patient does unexpectedly have a resistant organism causing pneumonia, the anticipatory regret of not leaving things as they were deters the change.

The patient was started on unfractionated heparin for intermediate (or low) risk DVT/PE, when LMWH is the preferred drug, because of the misguided worry that "an intervention may be needed." Even if that were a legitimate concern at the outset, the patient has made it through the night and has improved, yet UFH is continued, requiring those pesky aPTT checks and the unpredictable pharmacokinetics of the drug.

There are many more. Here's an omnipresent one on general medicine rounds (which I do as a "pulmonary hospitalists" every month or so). The patient was admitted with an exacerbation of chronic lung disease and "increased oxygen requirements." He has improved and is walking the floors but is not yet "back to baseline 2 liters." We have to keep the patient till he's back to baseline, the common reasoning goes. No, you don't. You execute a "consider the opposite" mental exercise, described in our paper and the perspective piece. You ask yourself, "if the patient had come to clinic in their current state, would I be calling to admit him?" If the answer is no, then the patient no longer warrants ongoing inpatient care and should be discharged.

The patient is on polypharmacy, with some dated medications, say atenolol, or even hydrochlorothiazide (the reason I consider it dated, and why it should not be "first line" are beyond the scope of this post). We restart them on discharge despite more modern and lower risk medications being available.

The patient has been on atorvastatin for years, but now has metastatic lung cancer and is unlikely to live 6 months, let alone time for the benefits of cholesterol lowering to accrue. Or, a nonagenarian woman with recurrent admissions for gait instability and falls is continued on her warfarin despite the risk benefit calculus having changed since she was started on it for atrial fibrillation 5 years prior. The status quo inures us to the poor result of the current risk benefit arithmetic. Alas, we are not performing that arithmetic: we "go with the status quo flow."

Another: the aforementioned patient with an exacerbation of chronic lung disease has an echocardiogram (or any other sundry test that is not immediately necessary for his care, and for which he would not have been admitted to get done as an inpatient). Should we keep him while awaiting the test? No. If the test is not necessary for his inpatient stay, it can and should be performed as an outpatient. I wager that this scenario alone adds a day on average to length of stay. It can be worse. Several such tests are awaited, but the weekend approaches. We (should) know that these tests are unlikely to be performed on the weekend, there's a Friday rush risking pushing them till Monday, then there's a Monday crunch to catch up for tests in queue from the weekend, some of which are necessary during an inpatient stay for other patients. Now we face the likely prospect of holding a patient for a test that is not going to be performed as an inpatient at all. We held him hoping for an unnecessary test that has a low(er) probability of even being performed.

There are other desiderata, of course: outpatient delays, logistics and transport (patient lives in the hinterlands). These must enter the decision calculus. But when we return to "consider the opposite" and create a holistic decision analysis considering all the probabilities and desiderata, we may realize that we are prolonging a hospitalization for the ECHO pipe dream, and we arrange outpatient ECHO. Or, we realize that the ECHO order was just another status quo, established by the admitting intern, in a patient who had a normal ECHO last year. Maybe he doesn't need that ECHO at all.