The sampling method can lead to biases. For example, when the sample is not representative. This could happen when population is not well targeted, the sample size is too low or the response rate of the survey is not sufficient.
There are methods to evaluate sampling errors in surveys conducted on a random sample of individuals. It is important to note that the sample variance is the indicator very commonly used to quantify sampling errors. Sampling errors are caused by the method of sampling and estimations used in the survey.