Availability bias is when we have the tendency to judge an event as more likely if it most readily comes to mind – for example, a patient with a history of abnormal vaginal discharge, fever and abdominal pain, seen after three other patients with pelvic inflammatory disease, is also likely to be diagnosed with pelvic inflammatory disease because of the relative ease that the diagnosis comes to mind. Another bias then comes into play with each subsequent healthcare professional that comes into contact with the patient – diagnostic momentum. Once a diagnosis has been made, the patient is effectively ‘labelled’ and team members continue this label. It is very difficult to remove the label and interpret symptoms with a fresh pair of eyes.
Anchoring bias is when we prematurely settle on a diagnosis or opinion based on a few features of the initial information or presentation. We fail to adjust our opinion as new information is presented to us. Anchoring bias is both related to and compounded by confirmation bias.
Confirmation bias is when having formed an opinion about a situation, we both favour and seek out evidence that supports our opinion, and overlook or discount contradicting evidence. As humans we are also more prone to confirmation bias if we are a novice as compared to an expert. Experts are more likely to modify their diagnostic assumptions earlier than novices.
For example, when reviewing an obese patient presenting at 36 weeks' gestation with a history of retrosternal chest pain, we should not seek evidence that this is gastroesophageal reflux, but instead disconfirm our theory by looking for alternative causes, such as acute coronary syndrome, aortic dissection or pulmonary embolism.
Watch the video below about confirmation bias in obstetrics. The examples here have been referenced to maternity care, but can be generalised to all areas of obstetrics, gynaecology and healthcare.
What is my rule?
Watch this video to learn a magic trick on how to teach others about confirmation bias.