TABLE 11-11 A Physician and President of a Tampa Health Maintenance Organization

TABLE 11-11
A physician and president of a Tampa Health Maintenance Organization (HMO) are attempting to show the benefits of managed health care to an insurance company. The physician believes that certain types of doctors are more cost-effective than others. One theory is that primary specialty is an important factor in measuring the cost-effectiveness of physicians. To investigate this, the president obtained independent random samples of 20 HMO physicians from each of 4 primary specialtiesGeneral Practice (GP) , Internal Medicine (IM) , Pediatrics (PED) , and Family Physicians (FP) and recorded the total charges per member per month for each. A second factor which the president believes influences total charges per member per month is whether the doctor is a foreign or US medical school graduate. The president theorizes that foreign graduates will have higher mean charges than US graduates. To investigate this, the president also collected data on 20 foreign medical school graduates in each of the 4 primary specialty types described above. So information on charges for 40 doctors (20 foreign and 20 US medical school graduates) was obtained for each of the 4 specialties. The results for the ANOVA are summarized in the following table.
-Referring to Table 11-11, what degrees of freedom should be used to determine the critical value of the F ratio against which to test for differences between the mean charges of foreign and US medical school graduates?

A) numerator df = 1, denominator df = 159
B) numerator df = 3, denominator df = 159
C) numerator df = 1, denominator df = 152
D) numerator df = 3, denominator df = 152