A sampling technique which splits the population into specific categories, or clusters. Every individual in the sample must be assigned to one of the clusters, but the population of each cluster can vary. A random sample of each cluster is then selected.
Example: A health questionnaire splitting the sample by how frequently they go to the gym – Regularly, Occasionally or Never.
A technique frequently used for market research, specific quotas are used.
Example: Ensuring 20 men and 20 women make up the sample of 40.
Similar to quota sampling, however individuals within each strata are randomly selected and strata sizes are kept in proportion with the overall population.
Example: 80% of a football teams supporters are male, so you ensure your sample of 10 has 8 males and 2 females.
Also referred to as opportunity sampling, a sample made up of the easiest people to reach. This method risks failing to produce a truly representative sample of the population.
Example: A company polling customers who are already subscribed on their mailing list.