A certain HMO is attempting to show the benefits of managed health care to an insurance company. The HMO believes that certain types of doctors are more cost-effective than others. One theory is that both primary specialty and whether the physician is a foreign or USA medical school graduate are an important factors in measuring the cost-effectiveness of physicians. To investigate this, the president obtained independent random samples of 40 HMO physicians, half foreign graduates and half USA graduates, from each of four primary specialties—General Practice (GP), Internal Medicine (IM), Pediatrics (PED), and Family Physician (FP)—and recorded the total per-member, per-month charges for each. Thus, information on charges were obtained for a total of
n = 160 doctors. The ANOVA results are summarized in the following table.
| Source | df | SS | MS | F Value | Prob > F |
| Specialty | 3 | 22855 | 7618 | 60.94 | .0001 |
| Medschool | 1 | 105 | 105 | 0.84 | .6744 |
| Interaction | 3 | 890 | 297 | 2.38 | .1348 |
Assuming no interaction, is there evidence of a difference between the mean charges of USA and foreign medical school graduates? Use
◦ No, because the test for the interaction is not significant at
, the test for the main effect for medical school is not valid.
◦ No, the test for the main effect for medical school is not significant at
.
◦ Yes, the test for the main effect for medical school is significant at
.
◦ It is impossible to make conclusions about the main effect of medical school based on the given information
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