sample size needed with a mean of 100,standard deviation of 20 for the the population of normal adults an iq range to fall between 2 iq points with 95% confidence interval
95% = mean ± 1.96 SEm
SEm = SD/√n
2 = 1.96 * 20/√n
Solve for n.
SEm = SD/√n
2 = 1.96 * 20/√n
Solve for n.