Pain is difficult to measure. Unlike using a thermometer to measure body temperature, a blood test to measure blood glucose, or a magnetic resonance imaging (MRI) scan to detect a tumour, there are no instruments or tests that objectively measure pain.
To understand why, one needs to understand what pain is.
Pain is a perception, and like other perceptions (such as happiness, sadness, anxiousness), it reflects the sum of a lot of external and internal information interpreted by our brains.
For example, we…