A Physician and President of a Tampa Health Maintenance Organization

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. 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 variable which the president believes influences total charges per member per month is whether the doctor is a foreign or US medical school graduate. 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. Which of the following tests will be the most appropriate to find out if the primary specialty and the origin of medical school degree interact to affect the charges?

A) Tukey-Kramer multiple comparisons procedure for one-way ANOVA
B) One-way ANOVA F test for differences among more than two means
C) One-way ANOVA F test for interaction effect
D) Two-way ANOVA F test for interaction effect