Miscellaneous Flashcards
How do you calculate the odds ratio (OR)?
Example dataset:
(a) Ill people who eat ice-cream (IIC): 13
(b) Ill people who do not eat ice-cream (InIC): 17
(c) Well people who eat ice-cream (WIC): 32
(d) Well people who do not eat ice-cream (WnIC): 23
- Divide conditions of group 1
- Divide conditions of group 2
- Divide the results of the divisions of each group
- IIC / InIC = x
a / c = x - WIC / WnIC = y
c / d = y - x / y = z , OR = z
- 13 / 17 = 0.76
- 32 / 23 = 1.39
- 0.76 / 1.39 = 0.54 (0.55 rounded up) , OR = 0.54
What does an odds ratio of exactly 1 mean?
Property A does not affect the odds of property B
What does an odds ratio of more than 1 mean?
There is a higher odds of property B happening with exposure to property A
What does an odds ratio less than 1 mean?
Lower odds
Risk ratio can also be called relative risk. TRUE or FALSE?
TRUE. Risk ratio and relative risk are the same thing.
How do you calculate relative risk (RR)?
Divide the category in question by the total number of the group for each category, then divide the answers.
For example:
100 obese people either have had a stroke (20) or have not had a stroke (80).
500 healthy people either have had a stroke (50) or have not had a stroke (500).
The risk of having a stroke if you are obese is 0.2 (20 / 100), compared to 0.1 (50 / 500) if you are healthy (not obese).
0.2 / 0.1 = 2
RR = 2
The RR of having a stroke if you are obese compared to if you are not obese is 2.
Obese people have twice the risk of having a stroke than healthy people.
Odds ratios (ORs) are important in case-controlled studies. TRUE or FALSE?
TRUE As in case-controlled studies it is not statistically appropriate to calculate RR.
Is it statistically appropriate to calculate RR (relative risk) in case-controlled studies?
No, it isn’t. The appropriate caculation is OR (odds ratio)
