Non probability

These methods, on the other hand, rely on human judgement.

Two of these methods are worth a mention:

Quota sampling, which works on the same principle as stratified sampling, to give a broad representation of the population. Quotas will be set on certain variables (e.g. age group, social class) and it is the responsibility of the field workers to obtain these quotas. This method is the most used consumer market research.

Postal surveys, which rely on the respondents to complete and return the questionnaire. A sampling frame will be used for administering the survey, but it is unlikely that all questionnaires will be returned. Non-response can be problematic - the researcher must first estimate its effect. Nevertheless, this method is frequently used.