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style="background-color:transparent;">In a study of the adverse effects of x-rays among children, a retrospective case-control study was done using records from several large children's hospitals for the period of 1980 to 1985. 10,000 children were selected as a representative population of ill children seen at the hospitals during that time. Subjects were classified according to whether or not they received an x-ray during their stay in the hospital and were followed from their hospital stay through 2005 for the development of cancer.

During the follow-up period, 49 incident cancers occurred in 3,263 children who had received an x-ray, and 47 incident cancers occurred in the 6,737 children who had not received an x-ray during their hospitalization.

-What is the risk ratio for the effect of exposure on the development of cancer in this study?

-What is the interpretation of this estimated ratio?

Match the following definitions to the correct term(s).

1-When investigators apply different eligibility criteria to the cases and to the controls in regard to which clinical conditions in the past would permit eligibility in the study.

2-Bias introduced by subjects who have developed a disease and who in attempting to answer the question "Why me?"

3-The result of an error in the design or conduct of a study.

4- When the means for obtaining information about the subjects in the study are inadequate so that as a result some of the information gathered regarding exposures and/or disease outcomes is incorrect.

5- Bias that leads to an erroneous estimate of the relative risk or odds ratio.

6-Bias that operates to enhance recall in cases compared with controls.

A.Exclusion Bias

B.Reporting Bias

C.Wish Bias

D.Researcher Bias


F.Recall Bias

G.Surveillance Bias

H.Information Bias

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