This lesson introduced us to ANCOVA methodology, which accommodates both continuous and categorical predictors. The model discussed in this lesson had one categorical factor and a linear effect of one covariate, the continuous predictor. We noted that the fitted linear relationship between the response and the covariate resulted in a straight line for each factor level, and the ANCOVA procedure depended on the condition of equal (or unequal) slopes. We saw one advantage of ANCOVA was the ability to examine the differences among the factor levels after adjusting for the impact of the covariate on the response.

The salary example comparing males and females after accounting for their years after college illustrated how software can be utilized when using the ANCOVA procedure. In the next lesson, the ANCOVA topic will be extended to include in the model up to a cubic polynomial relationship between response vs covariate.