A population is the total group of interest to the researcher or marketing manager. A sample is a smaller group, part of the relevant population. Because contacting an entire population typically isn t feasible, using a sample to represent the population is more practical. One method for meeting both needs is random sampling, where each member of the population has the same chance of being included in the sample. Confidence intervals refer to the range on either side of an estimate that is likely to contain the true value for the whole population.
Validity concerns the extent to which data measures what it is intended to measure.
Because the wording of a survey can lead to misunderstandings about what a question means, it is very important to construct questions carefully to ensure validity in subjects responses.