The t-test and z-test are both statistical methods used to compare sample data, but they are used in different scenarios depending on factors such as sample size and whether the population variance is known. Aspect T-Test Z-Test Population Variance Unknown Known Sample Size Small (typically n<30n < 30n<30) Large (typically n≥30n \geq 30n≥30) Distribution Used T-distribution Z-distribution (normal) Formula Uses sample standard deviation Uses population standard deviation Example Usage Comparing means of two small groups Comparing large sample proportions or means