In-class assignment (03/01/07)

 

Chi-square distribution: Table of the chi-square cutoff points at given degrees of freedom (df) and significance levels (area)

 

df\area

.995

.990

.975

.950

.900

.750

.500

.250

.100

.050

.025

.010

.005

1

0.00004

0.00016

0.00098

0.00393

0.01579

0.10153

0.45494

1.32330

2.70554

3.84146

5.02389

6.63490

7.87944

2

0.01003

0.02010

0.05064

0.10259

0.21072

0.57536

1.38629

2.77259

4.60517

5.99146

7.37776

9.21034

10.59663

3

0.07172

0.11483

0.21580

0.35185

0.58437

1.21253

2.36597

4.10834

6.25139

7.81473

9.34840

11.34487

12.83816

4

0.20699

0.29711

0.48442

0.71072

1.06362

1.92256

3.35669

5.38527

7.77944

9.48773

11.14329

13.27670

14.86026

5

0.41174

0.55430

0.83121

1.14548

1.61031

2.67460

4.35146

6.62568

9.23636

11.07050

12.83250

15.08627

16.74960

 

 

1. Suppose a new medicine and placebo were randomized between 100 patients. Among 40 patients who received placebo there were 20 positive responses, among those who used the new medicine positive response were registered for 35 people.

 

Please build two-by-two table, calculate different measures of association (ER, RR, and OR) together with their confidence intervals, and perform a Chi-square test of the null hypothesis of no association.

 

 

 

 

 

 

2. Suppose 10 patients were matched with controls in a 1 to 3 ratio. A clinically important binary outcome was measured for all the subjects. Positive response was registered for 6 patients (cases) and 8 controls. Which test(s) you would use for testing association. Why?

 

 

 

 

 

 

3. Suppose 180 patients agreed to participate in a study, 80 of them were in early 20s or younger, 30 are in the retirement age. Among 90 positive responses, 60 were registered in a group of young patients, 6 in the retirement group. Test the hypothesis that response to a treatment is different between different age groups.