Experimental design: generalization answers

In practice, the results of an experiment on a sample generalize only to the population that it represents

A sample of ten people at a checkout queue with tins of MoggyScoff in their shopping baskets represents the population ``people with a prior preference for MoggyScoff or with an inclination to try it at least once'', if it represents anything. While the result may be accurate for this population, it becomes increasingly difficult to trust as the population widens. As a cat food buyer, I am a member of the population ``people who need to buy cat food but with no particular preference for any given brand''. It is impossible to say to what degree the survey results generalize to my population.

This leads to the following principle:

A good experimental group will be chosen to represent the population which is of interest

Ideally, an experimenter will decide in advance for what population a result is required, and then select a sample that represents that population.