Beware of adding random numbers. This produces a predictable distribution that biases the sample. In the following distribution, you can see that the most common number generated by two fair dice is seven. The level of precision desired by the research dictates sample size. The degree of variation in the given characteristic will also contribute to the decision of sample size.
Smaller variation requires a larger sample.
In this example each specified category must have enough subjects for meaningful analysis. Sample Size, Non-probability Samples Saturation describes the point at which new cases do not add new information in qualitative research. Another stopping point for non-probability samples is the point of diminishing returns. That is, there may be more information available, but it is rare or inordinately difficult to obtain. In both, the population is divided into subgroups.