KEY FEATURES: Examples for each statistical expression help readers understand complex formulas A chapter on how to use the literature for power analysis walks readers through the process of making good assumptions A chapter on how to write about power analysis offers 7 key points on what needs to be included in a power analysis

# The Difference Between Two Groups in Simple Random Samples Where the Population Standard Deviation Must Be Estimated

### The Difference Between Two Groups in Simple Random Samples Where the Population Standard Deviation Must Be Estimated

In this chapter, we revisit the test about differences between group means, but now we acknowledge that the population standard deviation is unknown and must be estimated. This changes the distribution that we must use for the test and to determine power. We now must use the $t$ distribution instead of the standard normal distribution (Student, 1908). Since the $t$ distribution depends on the sample size, power analysis is less straightforward. In this chapter, we focus on the least squares regression method for testing for group mean differences. Doing this lays the ...