For assessment of current risk factors for developing toxic shock syndrome (TSS) during menstruation, a study was performed. Cases with onset between 1 January 1986 and 30 June 1987 were ascertained in six study areas with active surveillance for TSS. Age-matched controls were selected from among each patient's friends and women with the same telephone exchange. Of 118 eligible patients, 108 were enrolled, as were 185 "friend controls" and 187 telephone exchange-matched control.

This study was a:

A. prospective cohort study

B.case-control study

C.cross-sectional study

D.Randomized Controlled Trial

Results for tampon use as a risk factor:

Tampon Use	Menstrual Toxic Shock Patients	Friend Controls	Neighborhood Controls	Combined Controls
None	2	54	74	128
Any brand(s)	106	131	113	244
Total	108	185	187	372

What was the crude OR, when friend controls were used? [Hint: notice that those who used tampons were considered "Exposed".]

What was the crude OR, when neighborhood controls were used? [Hint: Again, notice that those who used tampons were considered "Exposed".]

What was the crude OR, when combined controls (friend controls + neighborhood controls) were used? [Hint: once more, notice that those who used tampons were considered "Exposed".]

Compare the OR obtained using Friend Controls to that obtained using Neighborhood Controls. Which one is lower?

A. OR obtained using Friend controls

or

B. OR obtained using neighborhood controls

Why?

A. Friends control were less likely to have used tampons than were neighborhood controls.

or

B. Friends control were more likely to have used tampons than were neighborhood controls.

or

C. Friends control were as likely to have used tampons than were neighborhood controls.

The use of friend controls vs. neighborhood controls in the study above is an example of:

A. Information Bias (misclassification of exposure)

B. Information Bias (misclassification of disease)

C. Medical surveillance/detection Bias

D. Selection Bias

E. Incidence-Prevalence Bias