Question

Using the data below calculate the risk difference, the risk ratio and the odds ratio. Discuss the overall results (Table 1) and the results of the cohort stratified by smoking. Discuss the estimates of risk difference, risk ratios, and odds ratios. Interpret and discuss the meaning of the stratified results.

		Gastric Cancer
		Yes	No
Smoke	Yes	150	150	30
	No	50	700	75

                                        

RD =

RR =                                                         OR=

You stratify by Smoking with the below numbers:

		Gastric Cancer
		Yes	No
Salt	Yes	100	100	50
	No	30	350	56

Population 1 - Smoke

                

                                                 

RD =

RR =                                                               OR=

        

Population 2 – No Smoke

		Gastric Cancer
		Yes	No
Salt	Yes	50	50	38
	No	20	350	70

RD =

RR =                                                               OR=

       

Answer 1

1) For Smoke:

Yes: Risk = 150 / 200 = 1.5

No: Risk = 150 / 850 = 0.1764

Relative Risk = 1.5 / 0.1764 = 8.5

Risk Difference = 1.5 - 0.1764 = 1.3236

Odds Ratio = (150/150) / (50/700) = 700/50 = 14

b) For Salt:

Yes: Risk = 100 / 130 = 0.7692

No: Risk = 100 / 450 = 0.2223

Relative Risk = 0.7692 / 0.2223 = 3.4601

Risk Difference = 0.7692 - 0.2223 =0.5469

Odds Ratio = (100 / 100) / (30 /350) = 11.667

c) For Gastic Cancer:

Yes: Risk = 50/70 = 0.7143

No: Risk = 50 / 400 = 0.125

Relative Risk = 0.7143 / 0.125 = 5.7144

Risk Difference = 0.7143 - 0.125 = 0.5893

Odds Ratio = (50 / 50)/ (20 /350) = 17.5