TABLE 13-9
It is believed that, the average numbers of hours spent studying per day (HOURS) during undergraduate education should have a positive linear relationship with the starting salary (SALARY, measured in thousands of dollars per month) after graduation. Given below is the Excel output for predicting starting salary (Y) using number of hours spent studying per day (X) for a sample of 51 students. NOTE: Only partial output is shown.

Note: 2.051E - 05 = 2.051*10⁻⁰⁵ and 5.944E - 18 = 5.944*10⁻¹⁸.
-Referring to Table 13-9, the 90% confidence interval for the average change in SALARY (in thousands of dollars) as a result of spending an extra hour per day studying is
A) wider than [-2.70159, -1.08654].
B) narrower than [-2.70159, -1.08654].
C) wider than [0.8321927, 1.12697].
D) narrower than [0.8321927, 1.12697].

Question

TABLE 13-9
It is believed that, the average numbers of hours spent studying per day (HOURS) during undergraduate education should have a positive linear relationship with the starting salary (SALARY, measured in thousands of dollars per month) after graduation. Given below is the Excel output for predicting starting salary (Y) using number of hours spent studying per day (X) for a sample of 51 students. NOTE: Only partial output is shown.
  
Note: 2.051E - 05 = 2.051*10⁻⁰⁵ and 5.944E - 18 = 5.944*10⁻¹⁸.
-Referring to Table 13-9, the 90% confidence interval for the average change in SALARY (in thousands of dollars) as a result of spending an extra hour per day studying is
A) wider than [-2.70159, -1.08654]. 
B) narrower than [-2.70159, -1.08654]. 
C) wider than [0.8321927, 1.12697]. 
D) narrower than [0.8321927, 1.12697].

Quizplus · Accepted Answer

The 90% confidence interval for the slope coefficient (the average change in salary for each extra hour of studying) is given by [0.8321927, 1.12697]. Since this is a one-to-one relationship, it is also the 90% confidence interval for the average change in salary for spending an extra hour per day studying. The margin of error for this interval is 0.147 so the interval is relatively narrow. Therefore, the correct answer is D - narrower than [0.8321927, 1.12697].

TABLE 13-9 It Is Believed That, the Average Numbers of Hours Spent