It's different for each test and intervention, and different again depending on why you're doing them. Balancing risk vs benefit is a major job of the doctor.

It's different for each test and intervention, and different again depending on why you're doing them. Balancing risk vs benefit is a major job of the doctor. One example: the humble chest X-ray. You may think the main risk is radiation, but IMO you'd be wrong to think that. The main risk is finding something. We call them incidentalomas. You would never have found it if you didn't do the CXR. It would never have caused you worry or morbidity. But now we know it's there, you need to get a lung biopsy. And that leads to a pneumothorax. That leads to a longer stay in hospital. That leads to time off work. You end up with no benefit to a patient who now has less trust in the medical system because they got a pneumothorax for nothing.