Investopedia contributors come from a range of backgrounds, and over 25 years there have been thousands of expert writers and editors who have contributed. Thomas J. Brock is a CFA and CPA with more ...

A t-test for population means compares the means between two populations. It is appropriate when the population standard deviations are unknown. This applet allows users to change the distributions of ...

A two-sample z-test for population means compares two population means. It is appropriate when the population standard deviations are known and the sample sizes are large. This web calculator conducts ...