The most important characteristic of a sample that makes it possible to generalize the results of a research study to the population from which the sample was selected is that it is, on average, representative of that population. Which of the following is most likely to ensure the sample is truly representative?

The sample is selected based on whether respondents possess minimal reading and writing skills enabling them to understand the questions presented on questionnaires

The entire population is included in the sample i.e. it is really a census

The sample is carefully screened to ensure that it contains, proportionately, people with the same demographic profiles as encountered in the population.

The sample is selected quickly, even at the risk of its being non-random to ensure that opinions are 'fresh.'

The sample is selected at random from the population of interest.