week 3 - measurements of association Flashcards
(23 cards)
Calculate the Rate Ratio in table 5.1 for
- Current smoker to have a stroke than a never smoker
- An ex smoker to have a stroke than a never smoker
A- 2.8 times
B- 1.6 times
Compared with non-smokers, calculate the rate difference in table 5.1 for
- Ex-smokers
- Current smokers
A- 10.2
B - 31.9
What is another name for a ratio measure?
Relative measure (relative risk)
When would you use rate ratio compared to risk ratio
Rate ratio is used when you compare two incidence rates. Risk ration is used when you compare two incidence proportions
The risk ratio for People who took aspirin to develop blood clots was 1.4. what does this mean?
This means that people who took aspirin were 1.4 times AS likely to develop blood clots, in other works people who took aspirin were 40% more likely to develop blood clots.
RRR in clinical trials stands for
Relative risk reduction – this is the same as relative risk and mainly used to see the effects of an intervention at reducing an outcome.
What are rate difference and risk difference sometimes referred to?
Excess risk and excess rate.
What is the incidence of natural occurrence of disease in an unexposed population often referred to?
Reference or background rate
What is rate difference sometimes called and how is it calculated?
Attributable risk. Calculated by the incidence rate in exposed group minus (-) incidence rate in the unexposed group.
The attributable fraction can also be referred to as….. and is calculated by….
Also referred to as the attributable proportion or the attributable risk percentage. It is calculated by Attributable risk (rate difference) divided by incidence in the exposed group.
In table 5.1 calculate the attributable fraction for current smokers to have a stroke and discuss what this denotes.
Attributable fraction = (49.6-17.7) divided by 49.6 = 0.64 = 64%
In other words of all the strokes occurring amongst current smokers about 2 thirds (64%) could be attributed to the fact the women currently smoked.
What is the attributable risk sometimes referred to as in clinical epidemiology?
Absolute risk reduction (ARR) or absolute risk increase (ARI) depending on whether the event rate is reduced or increased
What does population attributable risk (PAR) refer to and how is it calculated?
it is calculated by the total number of cases in the population minus (-) the total number of cases seen in a group on non-exposed people. And refers to how many extra cases can be attributed to the fact that some of the people in a population are exposed.
What is population attributable fraction sometimes referred to and how is it calculated? Calculate the PAF for table 5.1. and what does this percentage reflect?
Population attributable risk percent. Calculated by PAF = (population attributable risk divided by incidence in total population ) times 100. PAF for table 5.1 = (12.5/ 30.2) x 100 = 41%. 41% of strokes in the community can be attributed to smoking and in theory would not have occurred if no one had smoked.
in the below table calculate the relative risk, attributable risk and the attributable fraction (table 5.4.
What measure of association is used in a case-control study?
Odds ratio (OR)
For table 5.6 calculate the OR associated with use of the oral contraceptive pill in the development of ovarian cancer.
OR = (413/206) divided by (1160/ 322) = 0.56. in other words the odds of a case having used the OC pill are almost half of that compared to the odds of a control having used the OC pill.
What measure of association is often used in cross-sectional studies and why?
Despite cross-sectional studies measuring the prevalence of disease in different exposure groupsa prevalence ration (PR) is often difficult to work with and therefore an OR is often presented (sometimes referred to as prevalence odds ration (POR).
How is attributable fraction calculated in case-control studies?
AF = (OR-1)/OR x 100
how is population attributable fraction calculated in case- control studies?
See attached (Pe = prevalence of exposure amongst the cases)
Calculate the OR, AF and PAF for table 5.8 for the association of not wearing a helmet and head injury.
OR = 1.95
AF = 49%
PAF = 33.5%
when interpretting relative risk what factors do you need to give in your response.
need to comment on the exposure, risk, outcome and comparison exposure.
how do you calculate the number needed to treat (NNT) and what does it refer to
NNT = 1/Risk difference.
it refers to how many people you would need to treat before you see a reduction in the outcome.
