Tests that diagnose diseases are less reliable than you’d expect. Here’s why

You feel unwell, and visit your doctor. They ask some questions and take some blood for testing; a few days later they call to say you have been diagnosed with a disease.

What are the chances you actually have the disease? For some common diagnostic tests, the answer is surprisingly low.

Few medical tests are 100% accurate. Part of the reason is that people are inherently variable, but many tests are also built on limited or biased samples of patients – and our own work has shown researchers may deliberately exaggerate the effectiveness of new tests.

None of this means we should stop trusting diagnostic tests, but a better understanding of their strengths and weaknesses is essential if we want to use them wisely.

Article originally appeared on The Conversation Australia and New Zealand Sept 2023.