A virtual population. We frequently take measurements using a device, such as taking someone’s blood pressure or measuring air pollution. We know we could always take more measurements and get a slightly different answer, as you will know if you have ever taken repeat blood pressure measurements. The closeness of the multiple readings depends on the precision of the device and the stability of the circumstances – we might think of this as drawing observations from a virtual population of all the measurements that could be taken if we had enough time.
