when you conduct a survey, how do you know how many people is enough?
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It depends on a lot of factors, including the size of the effect you are trying to detect and the level of certainty you want to achieve. The size of the population you are studying doesn’t really matter unless it is so small (or your sample so large) that your sample takes in a large fraction of the population.
There will usually be biases that do not vary with sample size. For example, there is often a “social desirability bias”, in which people are less likely to give responses that are seen as embarrassing (e.g. admitting that they have cheated on partners). This will have the same effect on your results regardless of whether you ask 100 people or 1 million. So there are usually diminishing returns from increasing the sample size.
It’s also important to remember that in many types of research, the goal is not to collect statistical evidence but to understand particular people or perspectives in detail. Many researchers use qualitative methods such as in-depth interviews and focus groups to understand how people think and make decisions. It is not generally feasible to conduct these with large sample sizes. Similarly, doctors will often publish case studies about individual patients if there is something particularly unusual about them.
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