3. A university medical center urology group was interested in the association b

Question

3. A university medical center urology group was interested in the association between prostate-specific antigen (PSA, in mg/ml) and a number of prognostic clinical measurements in men with advanced prostate cancer. These prognostic indicators included cancer volume (cc) and seminal vesicle invasion (recorded as 1 for yes, 0 otherwise). Data were collected on 97 men who were about to undergo radical prostectomies. (A-10 pts.) PROC REG was run on the data, with resulting output given on Page 5 of this test. The variable psainv is defined to be the product psaxinvasion. According to this output, which variables are significant predictors of cancer volume at o-0.05? Which number(s) in the output did you use, and how did you use them to make your decision? (B-10 pts.) Keeping all three predictors, write an equation expressing the relationship between the independent variables psa, invasion, and (psa x invasion); and the dependent variable cancer volume. Then write separate equations for men with and without seminal vesicle invasion.

Explanation / Answer

A) psa has pvalue 0.0264 < 0.05 so we reject H0 at 5% l.o.s and conclude that psa(prostrate specific antigen) is significant predictor of cancer volume.

B) The regression line is given by

cancer volume = 0.05757 psa + 11.30846

(Note: No information or data is available to give separate regression lines for invasion and psa x invasion.)

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