Children's perception of reading difficulty. Table 28.15 contains measured and self-estimated reading ability data for 60 fifth-grade students randomly sampled from one elementary school.17 The variables are
(a) Is the relationship between measured (READ) and self-estimated (EST) reading ability the same for both boys and girls? Create an indicator variable for gender and fit an appropriate multiple regression model to answer the question.
(b) Fit a multiple regression model for predicting IQ from the explanatory variables LSS, READ, and EST. Are you happy with the fit of this model? Explain.
(c) Use residual plots to check the appropriate conditions for your model. (d) Only two of the three explanatory variables in your model in part
(b) have parameters that are significantly different from zero according to the individual t tests. Drop the explanatory variable that is not significant, and add the interaction term for the two remaining explanatory variables. Are you surprised by the results from fitting this new model? Explain what happened to the individual t tests for the two explanatory variables.