Question

1. Spasmodic dysphonia (SD) is an idiopathic, chronic, and disabling voice disorder. In a case-control study, 150 cases of SD were identified along with 150 controls. Of those with SD, 16 had previously experienced meningitis. Of the controls, 3 had previously experienced meningitis.
   1. What is the exposure and what is the disease?
   2. Set up the two by two table for these data with labels for exposures and disease status.
   3. Which measure of association/comparison should we use to assess the strength of the relationship between the exposure and disease?
   4. Calculate the correct measure and show your work.
   5. How do we interpret this effect estimate?

Answer 1

	Case(SD)	Control	Total
Exposed to meningitis	16	3	19
Non exposed to meningitis	134	147	281
Total	150	150	300

Case control studies start with disease. here exposure is meningitis and disease is spasmodic dysphonia.

The odds ratio is the measure of association for a case-control study. It tells us how much higher the odds of exposure is among cases of a disease compared with controls. The odds ratio compares the odds of exposure to the factor of interest among cases to the odds of exposure to the factor among controls.

Odds Ratio(OR)=Odds that a case was exposed/odds that a control was exposed

Odds that a case was exposed=16/134=0.119

odds that a control was exposed=3/147=0.020

OR=16/134 diivided by 3/147

0.119/0.020=5.95

If odds ratio is equal to 1 exposure is not associated with disease

If odds ratio is more than 1 exposure is positively associated with disease

If odda ratio is less than 1 exposure is negatively associated with disease

The further the OR is from 1 the stronger the association

Here there is strong association between exposure to meningitis and development of spasmodic dysphonia