Post by Admin on Feb 15, 2016 1:10:29 GMT
Twelve years ago, a lead poisoning clinic screened a number of local inhabitants for lead poisoning and found 110 people with the disease. To determine if living in public housing is a risk factor, a group of patients without lead poisoning was compared, and results are shown in the table below.
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Given the rarity of lead poisoning in the population studied, what are the odds of lead poisoing in individuals who lived in public housing, compared to those who lived in private housing?
A.
(100 x 4990)/(4700 x 10)
B.
(100/110)/(4700/9690)
C.
(100/4800)/(10/5000)
D.
(100/9800)/(10/9800)
E.
1 – ([100/4800]/[10/5000])
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A case-control study compares subjects who have a disease/outcome of interest (cases) with subjects who do not have the disease (controls) by going back retrospectively to evaluate the exposure (risk factor) in the groups. In a case-control study, the only comparison that can be done to evaluate a potential risk factor is the odds ratio, which is calculated as: (cases exposed to risk factor × controls not exposed) / (number of controls exposed to risk factor × number of cases not exposed).
Odd ratio is a measure of association and is defined as the ratio of the the odds that an outcome will occur in an exposed individual, compared to the odds that an outcome will occur in an unexposed individual. It is important to note that case-control studies cannot determine the incidence or prevalence of a disease and therefore that they cannot predict the risk of contracting that disease. Also remember that relative risk approaches odds ratio for small probabilities (ie, low prevalence studies).
B is not correct. 11% chose this.
This calculation is a distracter.
C is not correct. 28% chose this.
This is the relative risk, which can only be calculated in a cohort study. Cohort studies can either by prospective or retrospective. In cohort studies, the exposed and unexposed groups are followed longitudinally for the expected outcomes, in order to determine the actual proportion of the population affected by the outcome/disease.
D is not correct. 7% chose this.
This calculation is a distracter.
E is not correct. 7% chose this.
This is 1 - relative risk, and it represents the relative risk reduction, which is typically the result of the use of a medication. This can only be determined by prospective studies.
Bottom Line:
The correct answer is A. 47% chose this. In a case-control study, the best way to calculate the potential risk factor is by using the odds ratio.
Click to change
Given the rarity of lead poisoning in the population studied, what are the odds of lead poisoing in individuals who lived in public housing, compared to those who lived in private housing?
A.
(100 x 4990)/(4700 x 10)
B.
(100/110)/(4700/9690)
C.
(100/4800)/(10/5000)
D.
(100/9800)/(10/9800)
E.
1 – ([100/4800]/[10/5000])
We value your feedback!
A case-control study compares subjects who have a disease/outcome of interest (cases) with subjects who do not have the disease (controls) by going back retrospectively to evaluate the exposure (risk factor) in the groups. In a case-control study, the only comparison that can be done to evaluate a potential risk factor is the odds ratio, which is calculated as: (cases exposed to risk factor × controls not exposed) / (number of controls exposed to risk factor × number of cases not exposed).
Odd ratio is a measure of association and is defined as the ratio of the the odds that an outcome will occur in an exposed individual, compared to the odds that an outcome will occur in an unexposed individual. It is important to note that case-control studies cannot determine the incidence or prevalence of a disease and therefore that they cannot predict the risk of contracting that disease. Also remember that relative risk approaches odds ratio for small probabilities (ie, low prevalence studies).
B is not correct. 11% chose this.
This calculation is a distracter.
C is not correct. 28% chose this.
This is the relative risk, which can only be calculated in a cohort study. Cohort studies can either by prospective or retrospective. In cohort studies, the exposed and unexposed groups are followed longitudinally for the expected outcomes, in order to determine the actual proportion of the population affected by the outcome/disease.
D is not correct. 7% chose this.
This calculation is a distracter.
E is not correct. 7% chose this.
This is 1 - relative risk, and it represents the relative risk reduction, which is typically the result of the use of a medication. This can only be determined by prospective studies.
Bottom Line:
The correct answer is A. 47% chose this. In a case-control study, the best way to calculate the potential risk factor is by using the odds ratio.