One of the first steps of any market research study is to determine your sample size. This is a technical term that refers to the number of respondents you need to statistically represent the population you are surveying.
The sample size is an important feature of any research study where the goal is to make inferences about a population from a sample. In practice, the sample size used in a study is usually determined based on the cost, time, or convenience of collecting the data, and the need for it to offer sufficient statistical power. One of the most important considerations is how you want to analyze your data and what is the trade-off between confidence and cost.
If the sample of people you want to respond to your survey can all be considered as largely the same, or if you don't need to distinguish between different groups in your analysis, then you have one analysis group. In order to be confident in your results you need a robust sample size per analysis group. Therefore, if you wish to look at sub-groups within this analysis group (a simple example might be females and males, but could be generational splits, top and bottom buckets, etc.) then you will need to consider a sample size for each sub-group that is big enough to make decisions about.
What Sample Size Is Robust Enough?
As a beginning rule of thumb for general research studies, we suggest 300-500 respondents per analysis group, depending on population size. For concept testing, we recommend 150 respondents per concept.