How we change what others think, feel, believe and do
Non-proportionate quota sampling
Use when it is important to ensure that a number of sub-groups in the field of study are well-covered.
Use when you want to compare results across sub-groups.
Use when there is likely to a wide variation in the studied characteristic within minority groups.
Identify sub-groups from which you want to ensure sufficient coverage.
Specify a minimum sample size from each sub-group.
A study of the prosperity of ethnic groups across a city, specifies that a minimum of 50 people in ten named groups must be included in the study. The distribution of incomes across each ethnic group is then compared against one another.
In proportionate quota sampling, the sample size from each sub-group is proportionate to the size of the sub-group in relation to the overall the population. The non-proportionate method does not do this balancing, perhaps because the exact proportions are not known.
In the proportionate method, if the sub-group is 2% of the population and 100 people are being studied, it may be feared that sampling only 2 people in a group may gives results that are not typical for that group. A minimum of 10 people taken from each sub-group would reduce the chance of non-typical people biasing the results.
Care must be taken in drawing conclusions from the study. Given the disproportionate quota in each group, it would be incorrect to treat the results as proportionate.