The sample size is the portion of a population that is included in your research. For formula purposes, the sample size is represented by the lower-case letter n, and the size of the population as a whole is indicated by upper-case N. Calculating a correct sample size will help provide you with accurate testing results. The level of precision, the level of risk and the degree of variability are all factored in to determine the best sample size for you research. To determine sample size a formula can be used combining all of this information.
Square the level of risk. Level of risk is equal to 1.96. So, 1.96x1.96 = 3.84.
Multiply 3.84 by the degree of variability times one minus the degree of variability. The degree of variability is represented by p. So, 3.84 x p(1-p).
Divide your answer from step two by the margin or error squared. Margin of error is represented by the letter m. Your equation should look like this: ( 3.84 x p[1-p]) / m^2 ). The solution will provide a sample size for a simple random sample.
A census, a sample size from a similar study or published sample size tables can also be used in determining sample size.