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Old 07-11-2011
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Stats Compromising the Control Group in Case-Control Study

Officials of a large community hospital report an increased incidence of Acute Myelogenous Leukemia (AML) among children aged 5-12. They observe that some households in the community are exposed to chemical waste from a nearby factory & worry that the waste causes leukemia. If a case-control study is designed to evaluate the hospital officials' claim which of the following subjects are most likely to compromise the control group?

A) Children who are exposed to the chemical waste who do not suffer from AML.
B) Children who are not exposed to the chemical waste who do not suffer from AML.
C) Children from the outpatient clinic in the area who do not suffer from AML.
D) Children who are not exposed to the chemical wastes who suffer from AML.
E) Children who suffered from AML but were cured.
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C) Children from the outpatient clinic in the area who do not suffer from AML.
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Old 07-11-2011
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Quote:
Originally Posted by bebix View Post
C) Children from the outpatient clinic in the area who do not suffer from AML.
Can you please give me an explanation for it? I thought the answer was D so I thought I would start a discussion on here! lol
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Old 07-11-2011
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Quote:
Originally Posted by Hope2Pass View Post
Can you please give me an explanation for it? I thought the answer was D so I thought I would start a discussion on here! lol
Case-control
You start the study with people with the disease (case) and w/out the disease (control)...independent of whether or not they were exposed (this variable is not taken into account, otherwise you will have selection bias).

In a Cohort study
You start the study with an exposed group and an unexposed group...100% of the participant dont have the disease.
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Old 07-11-2011
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Quote:
Originally Posted by bebix View Post
Case-control
You start the study with people with the disease (case) and w/out the disease (control)...independent of whether or not they were exposed (this variable is not taken into account, otherwise you will have selection bias).

In a Cohort study
You start the study with an exposed group and an unexposed group...100% of the participant dont have the disease.

Thanks a lot!
Just one question - If the variable of exposure to the risk factor is not taken into consideration then how do u correlate to it in the study?
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Originally Posted by Hope2Pass View Post
Thanks a lot!
Just one question - If the variable of exposure to the risk factor is not taken into consideration then how do u correlate to it in the study?
"this variable is not taken into account, otherwise you will have selection bias"...only when you create the groups...so, you start with the outcome (disease/no disease) and then, you look back in time to learn which subjects in each group had the exposure(s), comparing the frequency of the exposure in the case group to the control group.
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Oh ok thanks. Makes sense now
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I think it should be a
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Quote:
Originally Posted by usluipek View Post
I think it should be a

Case-control:
We start with the outcome (disease/no disease) and then, we look back in time to learn which subjects in each group had the exposure(s), comparing the frequency of the exposure in the case group to the control group (OR).

A) Children who are exposed to the chemical waste who do not suffer from AML. = 100% of children have been exposed and dont have the disease = Selection bias (in the control group)

B) Children who are not exposed to the chemical waste who do not suffer from AML. = = 100% of children havent been exposed and dont have the disease = Selection bias (in the control group)

C) Children from the outpatient clinic in the area who do not suffer from AML. = control

D) Children who are not exposed to the chemical wastes who suffer from AML. = 100% of children disease / no exposed = Selection bias (in the cases group)

E) Children who suffered from AML but were cured. = 100% of children had the disease = they are potential cases
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  #10  
Old 07-11-2011
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I think it is A.
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Quote:
Originally Posted by heman466s View Post
i think it is A.
...the correct answer is C)....

A) is a classic example of Selection bias!
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Default 2 x 2 table

here is the same idea...using a 2 x 2 table

bias.bmp
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Old 07-11-2011
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I misread the question, missed the word "compromise"
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Further to the question, if we have to select the best control group from the answers, which one should we pick?
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Quote:
Originally Posted by usluipek View Post
I misread the question, missed the word "compromise"
itīs just a typo...should say comprise...
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Quote:
Originally Posted by usluipek View Post
Further to the question, if we have to select the best control group from the answers, which one should we pick?
so, the best answer....if you have to create an unbiased control group is C)....
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Old 07-11-2011
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this question is from uworld and they have also explained it pretty good..
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C children from the area who do not suffer from
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Old 07-12-2011
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Default Answer D ?

Quote:
Originally Posted by Hope2Pass View Post
Officials of a large community hospital report an increased incidence of Acute Myelogenous Leukemia (AML) among children aged 5-12. They observe that some households in the community are exposed to chemical waste from a nearby factory & worry that the waste causes leukemia. If a case-control study is designed to evaluate the hospital officials' claim which of the following subjects are most likely to compromise the control group?

A) Children who are exposed to the chemical waste who do not suffer from AML.
B) Children who are not exposed to the chemical waste who do not suffer from AML.
C) Children from the outpatient clinic in the area who do not suffer from AML.
D) Children who are not exposed to the chemical wastes who suffer from AML.
E) Children who suffered from AML but were cured.
The claim is - waste is the cause of AML; null hypothesis - waste does not cause AML. To reject we need to check a AML occurance in the group not exposed to waste - D....
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Old 07-13-2011
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Default what is the answer?

what is the correct answer? Thank you.
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  #21  
Old 07-13-2011
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correct answer is C.
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