External Validity

This refers to the extent to which the results of a study can be generalized or extended to others. For example, if a study on a drug is only conducted on white, middle aged, overweight, women with diabetes, can the results of the study be generalized to the rest of the population? Are the results only valid to the population studied? Researchers go to great lengths to select a group of people for the study (a sample) that is representative enough that the results can be extended to lots of people.