An investigator is interested in studying the relationship between radiation exposure and development of gastrointestinal (GI) tumors.He assembles a cohort of cancer-free subjects, divides them into "high" and "low" radiation exposure groups, and follows them over 10 years for evidence of GI tumors.

1. Suppose that the investigator uses a diagnostic test that fails to identify 20% ofallGI tumors but never registers a false positive result (i.e. no one without the cancer is ever misdiagnosed as having cancer).Describe this situation in terms of sensitivities and specificities for the exposed and unexposed subjects:

Sensitivity (D | E)=Sensitivity (D | not E)=

Specificity (D | E)=Specificity (D | not E)=

The following summarizes the data from the SOURCE population (no misclassification):

High Radiation

Low

Radiation

Total

GI Tumor

600

200

800

No Tumor

1400

1300

2700

Total

2000

1500

3500

1. What is the unbiased estimate of the risk ratio (RR)?
2. Use the sensitivities and specificities from part a to show the data that would have been observed by the investigator:

High Radiation

Low Radiation

Total

GI Tumor

No Tumor

Total

1. Calculate the observed RR.Is there no bias, bias toward the null, bias away from the null, or switchover bias?
2. The following table summarizes the OBSERVED data from adifferentstudy of radiation and GI tumors:

High Radiation

Low Radiation

Total

GI Tumor

476

376

852

No Tumor

524

624

1148

Total

1000

1000

2000

Assuming the scenario described in part "a" above, what is the corrected (unbiased) estimate of the RR for the relationship between radiation exposure and GI tumors for this study?Show your calculations.What is the nature of the bias, if any?

1. Calculate an odds ratio (rather than a RR) for both the observed and corrected data in part e.Is your conclusion regarding bias the same?