contingancy tables

Question 1

What is a contingancy table used for

Answer 1

To determine association between two categorical variables

Question 2

what methods of presenting the information from contingancy tables can we use

Answer 2

Relative risk
Risk difference
Odds ratio

Question 3

How to calculate the relative risk

Answer 3

preportion exsposed +disease /proportion not exposed and diseased
concvention = exposed/not exposed
if greater than 1 then exposure increases, if equal 1 exposure doesnt impact, if less than 1 exposure decreases

Question 4

How to calculate the risk difference

Answer 4

proportion exposed + diseased - propostion notexposed + diseased
if multipled by 100 gives the difference in the numebr of people expected to be a case given exposure

Question 5

How to calculate the odds difference

Answer 5

OD = a/b/c/d = ad/cb, therefore the OD is irrespected of columns and rows and can be used in situations when there values have been determined by the investigator such as RCT or case controled

Question 6

When can OD and RR be very simlar

Answer 6

When talkinga bout a rare disease then the denominator of proportions for B and B+A will be very simlar due to A (disease rate) being very small compaired to B (not-diseased) in each group

Question 7

How can the odds difference be interpreted

Answer 7

1) if exposed odds of being a case is X%
2) if a case odds of you being exposed is X%