Most statistical studies are based on a sample of the population at large. The relationship between a population and sample is shown in Figure 12.1 (and also described in Chapter 1).
The relationship between a population and sample.
Why not just measure the whole population rather than rely on only a sample? That’s a very good question! Depending on the study, measuring an entire population could be very expensive or just plain impossible. If I want to measure the life span of a certain breed of pesky mosquitoes (extremely short if I had any say in the matter), I could not possibly observe every single mosquito ...