Question

Part 4: Relationship between Risk Ratlo and Odds Ratos. Use the data in tables 1 and 2 to calculate the risk and odds rabios. Table 1 Melkoobacter pylori infection and development of stomach cancer as e disease in a Hypothetical Population of 10,000 Persons Disasset Stomach-Cancer No Diseasa No-Stomach Cancer b=1,975 Totale 2,000 225 Exposed (H. pylor infection) Not Exposed (No H. pylori Infection) Total L d=7,995 8,000 812 9.970 10.000 Table 2 Helicobacter pylori infection and development of stomach cancer as a common disease in a Hypothetical Population of 10.000 Persons Disease Stomach Cancers a=1,000 No Disease No Stomach Cancera b=1.000 d=7.800 Total 2,000 Exposed (H. pylor infection) Not Exposed No H. pylori infection) c=200 8.000 Totale 1.2001 8.800 10,000 1. Risk Ratio a. Table 1: b. - Table 2: 2. Odds Ratio: 1 a. Table 1:1 b. Table 2: 3. Compare the Risk Ratio to the Odds Ratio for table 1 and then compare the Risk Ratio to the Odds Ratio for table 2. Describe these comparisons and the reasons for the differences/similarities (see the interpretation of the Odds Ratio section in the folder in the loaming materials for this week): Pace Breas

Answer 1

1.Risk Ratio

a).Risk ratio can be calculated simply by dividing the cumulative incidence in exposed group by cumulative incidence in unexposed group.

That is For table 1.

[(25/2000)*100]=1.25

[(5/8000)*100]=0.0625

RR=1.25/0.0625=20

b).For table 2.

[(1000/2000)*100]=50

[(200/8000)*100]=0.25

RR=50/0.25=20

2.Odd Ratio

Odd ratio is calculated by dividing the odd of the first group by the odds of the second group.

That is (a*d)/(b*c)

a).For table 1.

(25*7995)/(1975*5)=20.240

b).For table 2.

(1000*7800)/(200*1000)=39

3).odd ratio and risk ratio (Relatively risk ratio ) have unique concepts.Odd ratio is the ratio of two odds whereas risk ratio is the ration of two probabilities.

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