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Old 10-28-2011
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Stats What type of Bias!

A study is conducted to determine the association between cigarette smoking and the rate of motor vehicle collision. The first group consist of 1000 current cigarette smokers,the second group consists of 800 former cigarette smokers and the third group consists of 750 people who have never smoked cigarettes.
All three groups contain participants of both genders that are from various ethnic backgrounds. The data collected show a higher rate of motor vehicle collisions among current smokers than for non smokers over the 4 year period of study (p < .05), but the rate is not statistically different from that for the former smokers (p >0.05). Which of the following raises the most concern about the validity of the study results?

A. Expectancy Bias
B. Late look Bias
C. Measurement Bias
D. Proficiency Bias
E. Recall Bias
F. Selection Bias

Please answer with eXPLANATION
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Old 10-29-2011
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I think this was part of one of my Kaplan Step 1 Qbank Ques.

learnt it like this,


First determine which type of study it is.. and then based on that go for the bias:

here is it a cohort study.. i.e its observational and prospective (4 yrs). for a cohort study LINK it to Selection Bias.

For a case-control ( i.e Retrospective), since they need to go back in time they will have RECALL BIAS.
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Old 10-29-2011
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F. Selection Bias i think for cohort study
hard q
plz post the answer
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Old 10-29-2011
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Quote:
Originally Posted by USMLE2011m View Post
I think this was part of one of my Kaplan Step 1 Qbank Ques.

learnt it like this,


First determine which type of study it is.. and then based on that go for the bias:

here is it a cohort study.. i.e its observational and prospective (4 yrs). for a cohort study LINK it to Selection Bias.

For a case-control ( i.e Retrospective), since they need to go back in time they will have RECALL BIAS.
good way to remember things friend, but I assure you things do not always go like that cuz most types of bias can affect any study (except case report and series of course)
I am not sure about the answer of this question but I agree with you that cohort have more concerns about selection and it really appears that it is the number of the patients selected and/or the type of control groups used are causing the bias in this particular study
Thus, I would go for answer F, selection bias
My explanation is that the smaller number in the 3rd group (750) was not enough and that if it was increased to be more close to the study group ( smokers; 1000) the results might have shown no significant differences (like that in the 2nd group (ex-smokers, 800) in which the number of patients was closer to the study group
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Old 10-29-2011
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Quote:
Originally Posted by USMLE2011m View Post
I think this was part of one of my Kaplan Step 1 Qbank Ques.

learnt it like this,


First determine which type of study it is.. and then based on that go for the bias:

here is it a cohort study.. i.e its observational and prospective (4 yrs). for a cohort study LINK it to Selection Bias.

For a case-control ( i.e Retrospective), since they need to go back in time they will have RECALL BIAS.
Thanks Selection Bias is the answer and the same way its explained in the Qbank.

I thought it too be late look bias . But yes now this is sinking in that in questions like this we need to see about the type of study and then lock our choice.
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