For the following calculations, use the results in column (4) of Table 13.2. Consider two classrooms, A and B, which have identical values of the regressors in column (4) of Table 13.2 but differ as noted:

a. Classroom A is a small class, and classroom B is a regular-sized class. Construct a \(90 \%\) confidence interval for the expected difference in average test scores.

b. Classroom A has a teacher with 5 years of experience, and classroom \(B\) has a teacher with 10 years of experience. Construct a \(90 \%\) confidence interval for the expected difference in average test scores.

c. Classroom A is a small class with a teacher with 5 years of experience, and classroom B is a regular-sized class with a teacher with 10 years of experience. Construct a \(90 \%\) confidence interval for the expected difference in average test scores. In STAR, the teachers were randomly assigned to the different types of classrooms.

d. Why is the intercept missing from column (4)?

Table 13.2

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(1) 13.90 TABLE 13.2 Project STAR: Differences Estimates with Additional Regressors for Kindergarten Regressor Small class (3) 15.93 (4) 15.89 (2) 14.00 (4.23) [5.48,22.32] (4.25) [5.55,22.46] (4.08) (3.95) [7.81,24.06] [8.03, 23.74] Regular-sized class with aide 0.31 -0.60 1.22 1.79 (3.77) [-7.19, 7.82] (3.84) [-8.25, 7.05] (3.64) [-6.04, 8.47] (3.60) [-5.38,8.95] Teacher's years of experience 1.47 (0.44) [0.60, 2.34] 0.74 (0.35) [0.04, 1.45] 0.66 Boy (0.36) [-0.05, 1.37] -12.09 (1.54) -34.70 Free lunch eligible Black Race other than black or white School indicator variables? R Number of observations (2.47) -25.43 (4.52) -8.50 (12.64) no no yes yes 0.01 0.02 0.22 0.28 5786 5766 5766 5748