Question

A case-control study examining the influence of sexual behaviour on Hepatitis B was conducted in a Vancouver hospital between 2005 and 2008. The study recruited 229 Cases with Hepatitis B and 229 age- and sex-matched Controls. Both the Cases and Controls completed a questionnaire that inquired about the number of sexual partners they had in the past 2 years. Their responses were used to create the following exposure groups: 0 sexual partners (N=87), 1 sexual partner (N=257), and 2 or more sexual partners (N=114). Of the 229 Cases, 15 were in the 0 sexual partners group, 134 were in the 1 sexual partner group, and 80 were in the 2 or more sexual partners group.

Question 31 options:

A)70%

B) 5.23

C) 50%

D) 11.3

*Match the numbers above to the statements below.

1.	The prevalence of Hepatitis B in the 458 study participants was
2.	The prevalence of Hepatitis B in those with 2 or more partners was
3.	The odds ratio for Hepatitis B in the group with 1 sexual partner by comparison to the group with 0 sexual partners was
4.	The odds ratio for Hepatitis B in the group with 2 or more sexual partners by comparison to the group with 0 sexual partners was

Answer 1

	partner	case	control	total
	0	15	72	87
	1	134	123	257
	2	80	34	114
	total	229	229	458

1)

The prevalence of Hepatitis B in the 458 study participants was = (229/458) *100 = 50%

2)

The prevalence of Hepatitis B in those with 2 or more partners was = (80/114) * 100 =70%

3)

The odds ratio for Hepatitis B in the group with 1 sexual partner by comparison to the group with 0 sexual partners was =

= (134/123)/(15/72) = 5.23

4)  The odds ratio for Hepatitis B in the group with 2 or more sexual partners by comparison to the group with 0 sexual partners was = (80/34)/(15/72) = 11.3