248 PART 5 Looking for Relationships with Correlation and Regression

Unfortunately, that is not possible in practice, because the equations would be too

complicated. Instead, considerations are aimed more toward being able to gather

enough data to support a planned regression model. Imagine that you plan to

gather data about a categorical variable where you believe only 5 percent of the

participants will fall in a particular level. If you are concerned about including that

level in your regression analysis, you would want to greatly increase your estimate

for target sample size. Although regression models tend to converge in software if

they include at least 100 rows, that may not be true depending upon the number

and distribution of the values in the predictor variables and the outcome. It is best

to use experience from similar studies to help you develop a target sample size

and analytic plan for a multiple regression analysis.