Question

Question 1

The association between cellular telephone use and the risk of brain cancer was investigated in a case-control study. The study included 475 cases and 400 controls and the following results were seen:

		Cases	Controls
Cellular Phone User	Yes	270	200
	No	205	200
	Total	475	400

Calculate the odds ratio based on these data.

The p value for this odds ratio is 0.06. State your interpretation of this p-value.

Gender was considered a potential confounder and effect measure modifier in this study. The data were stratified into males and females in order to assess these issues.

	Males				Females
		Cases	Controls			Cases	Controls
Cellular Phone User	Yes	242	150		Yes	28	50
	No	100	50		No	105	150

Answer 1

OR (Cases)=Number of favourable outcome/Number of unfavourable outcome = = 270/205=1.32:1

and Odds (Control)=200/200=1:1

OR=Odds of intervention group/Odds of Control group=1.32/1=1.32:1

• The p value is not less than 0.05. Therefore, there is not statistically significant difference between cases and control group.

OR(Males cases)=242/100=2.42:1 and OR ( Males control)=150/50=3:1

OR=2.42/3=0.81:1

• The OR is less than 1, intervention is better than control

OR(Females cases)=28/105=0.27:1 OR (Female control)=0.33:1

OR=0.27/0.33=0.82:1

• The OR is less than 1, intervention is better than 1.

Therefore, gender is a confounder in the study. Because, in second case (stratum based odds ratios) the intervention is found to be better than control, compared to first case, where control was found to be better than intervention.