Answers to Quiz Six

1a.  The expected value for the case exposed cell is (90 x 100)/300 = 30.

Solve for the other expected values by subtraction.

                            Case   Control
                   Exp       30      60
                   Not exp   70     140

b.  The test statistic equals (40-30)sq/30 + (50-60)sq/60 + (60-70)sq/70 +
(150-140)sq/140 = 7.14.  Reject the null hypothesis with p < .01.

c.  The odds ratio equals (40 x 150)/(60 x 50) = 3.0.

d.  The two sample test of proportions equals (.4 - .25)/sqrt(.3 x .7 x
(.01 + .005)) = 2.67.  Reject the null hypothesis with p < .01.