The size of the standard error is affected by two values. The first is the standard deviation of the population. The larger the population standard deviation, … , the larger … / . If the population is homogeneous, resulting in a small population standard deviation, the standard error will also be small. However, the standard error is also affected by number of observations in the sample. A large number of observations in the sample will result in a small standard error of estimate, indicating that there is less variability in the sample means.
We can summarize the calculation for a 95% confidence interval using the following formula: