Factors Influencing Sample Size Include
1) Prevalence of particular event or characteristics- If the prevalence is high, small sample can be taken and vice versa. If prevalence is not known, then it can be obtained by a pilot study.
2) Probability level considered for accuracy of estimate- If we need more safeguard about conclusions on data, we need a larger sample. Hence, the size of sample would be larger when the safeguard is 99% than when it is only 95%. If only a small difference is expected and if we need to detect even that small difference, then we need a large sample.
3) Availability of money, material, and manpower.
4) Time bound study curtails the sample size as routinely observed with dissertation work in post graduate courses.