Online classe Monday, April 12, 14h30-17h00

[slides 343-370] Some final comments regarding the ANOVA context. The Analysis of Covariance (ANCOVA): the general ideia. A detailed study of the ANCOVA model to compare different simple linear regressions in k contexts defined by the k levels of a factor: the concept, notation and terminology; the full ANCOVA model allowing for different regression lines in each factor level and its relation to the simple linear regression models fitted only with the subset of the data for each factor level. Submodels of interest, resulting from different hypotheses regarding the parameters of the full ANCOVA model. The role of partial F and Student's-t tests in choosing an appropriate model. An example with the iris dataset, relating Petal.Length and Sepal.Length: the full ANCOVA model assuming different regression lines in the factor levels; the model assuming parallel lines, but possibly different intercepts; and the single regression line model; choosing the model. A warning about the model assumptions. A formula relating the coefficients of determination of the ANCOVA model and of the individual simple regressions in each factor level. A word on more general contexts. ANCOVA Exercise 1.