Question 6 [3+4+1=8 points] The data in the files beetles. xls, beetles.csu and beetles. txt show the number of insects killed after exposure to var- ious (standardized) doses of an insecticide. 6.1 Fit a logistic regression model to the data with dose and (dose)2 as covariates. Write the values of the three coefficient estimates here: intercept dose (dose)2 6.2 Use marginal model plots to assess the quality of the fit. Show a rough freehand version of one of the plots and indicate the relevant feature(s) on it that point(s) to a satisfactory or unsatisfactory fit. 6.3 Use the Wald statistic to test at the 1% level of significance whether the estimated coefficient of (dose)2 is statistically significantly different from zero