A recent case-control study assessed the relationship of hepatitis C virus (HCV) infection to B-cell non-Hodgkin lymphoma (B-NHL). Cases of B-NHL were identified in the hematology department wards of 10 hospitals located in different cities throughout the United States. The control group consisted of on B-NHL patients admitted to other departments of the same hospitals. (e.g. ophthalmology, general surgery, internal medicine etc). For both cases and controls, only patients with newly diagnosed diseases were included in the study. Testing for HCV was done after cases and controls were hospitalized.

Age (years) Cases Controls
Number HCV Positive Number HCV Positive
<= 55 163 18 231 6
> 55 237 52 165 16

1) What type of case-control study have the authors conducted?
2)Calculate the exposure odds ratio reflecting the HCV/B-NHL association for each group.
3) Describe (in words) the meaning of the OR for the age group >55 yeas.
4) What is an important short coming of the study?