POPM 3240 Study Guide - Quiz Guide: Relative Risk, Cohort Study, Null Hypothesis
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21 Oct 2016
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Ratio of the probability of getting the disease with exposure to probability of getting disease without exposure. This is good for a cohort study where you know has been exposed to risk factor a(cid:374)d (cid:449)ho has(cid:374)"t! Non-exposed a c a+c b d b+d a+b c+d n = a+b+c+d. Rr = incidence in exposed / incidence in non-exposed = (a/a+b) / (c/c+d) Rr = 1 no difference between exposed and non-exposed. Rr > 1 exposed have greater risk, positive association, may be causal. Rr < 1 non-exposed have greater risk, negative association, may be preventative (ex. vaccines) Example: relative risk of 2 means the exposed group has two times the risk of disease than the non-exposed group. Odds of exposure in the diseased group / odds of exposure in the non-diseased group. Good for cohort studies: start with exposures and then look at outcome. Odds of disease in exposed are x times the odds of disease in the non- exposed.
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- Compute the Person-Years of smoking exposure using the tablebelow. (Hint: add the years at risk of throat cancer (TC) â seeexamples).
- Once they develop TC they are no longer at risk and their yearsin the study canât be counted.
- Add each personâs years of exposure in the right column andenter the value in the box next to âTotal P-Y at Risk of ThroatCancerâ.
- Then count the P-Y at risk for the Current/Former Smokers(exposed) and the P-Y at risk for the Never-Smokers (notexposed)
- Using the Person-Years for each exposure group as thedenominator and the number of TC recorded for each exposure group;compute the Incidence Density for TC risk in current/former smokers(exposed) (IDE) & compute the incidence density forTC risk in never smokers (not exposed) (IDNE).
- The compute the Incidence Density Ratio (also call RR), dividethe IDEby the IDNE. This value is interpretedthe same as the Relative Risk.
Years in the Study at Risk of Developing ThroatCancer | Years at Risk | |||||||||
Person | Smoker | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | |
A | Yes | at risk | at risk | TC | No longer at risk of throat cancer | 2 | ||||
B | No | at risk | at risk | at risk | at risk | at risk | at risk | at risk | at risk | 8 |
C | No | |||||||||
D | Yes | TC | ||||||||
E | Yes | TC | ||||||||
F | No | |||||||||
G | No | TC | ||||||||
H | No | TC | ||||||||
I | Yes | TC | ||||||||
J | Yes | TC | ||||||||
Total P-Y at Risk of Throat Cancer |
- Sum the Person-Years of Exposure for each exposure group? (1point)
Former/Current Smoker (1/2 point)
Never Smoker(1/2 point)
- How many of the exposed & not exposed participantsdeveloped throat cancer (1 point)?
Former/Current Smoker (1/2point):
Never Smoker(1/2point):
- What is the Incidence Density for the exposed (IDE)and non-exposed (IDNE) groups? (1 point)
Former/Current Smoker (1/2point):
Never Smoker (1/2 point):
- Compute the Incidence Density Ratio (IDR). Is the IDRprotective or hazardous? (1 point).
10. Using the interpretation for Relative Risk onpage 120 of your text, interpret the meaning of the IncidenceDensity Ratio (1 pt):