Question

 

PART IV - ANALYSIS AND INTERPRETATION OF EPIDEMIOLOGIC RESULTS

The following food exposure information was collected through the cohort study. On January 19, the information was tabulated by epidemiologists from the Argentine MOH. (Table 2)

Table 2. Foods eaten by ill and well bus drivers at the home at the terminal bus stop, January 3-7, 1998. (N=21)

Food item	Ate item		Did not eat item
	Ill	Well	Ill	Well
Bologna	1	0	8	12
Hot dog	1	1	8	11
Matambre*	9	2	0	10
Mate**	4	4	5	3
Processed Ham	2	3	7	9
Sauce	7	2	2	10
Salami	1	1	8	11
Solid ham	2	3	7	9

*Matambre is a traditional meat roll in Argentina.

**Mate is green tea.

Question 12: Calculate the appropriate measures of association for these exposures.

Question 13: Interpret the results. What further data analysis/information might help?

Answer 1

12) Appropriate measure of association in a cohort study is the relative risk. From the relative risk we can determine the excess risk of disease in the exposed group compared with the unexposed group. To find the relative risk we have to find the ratio of the attack rates of the disease among people exposed to the factor & those who are not exposed to that factor. The attack rate is the incidence of disease in a group divided by the total number of people in the group.

Attack rate = Number of ill people in group/ Number of people in group

Relative risk = Attack rate for exposed persons/ Attack rate for unexposed persons

= Number of ill persons who ate item/ Total number of persons who ate item                          

   Number of ill persons who did not eat item/ Total number of persons who did not eat item

Food Item	Ate Item			Didn't Eat Item			Relative Risk
	Ill	Well	Attack Rate	Ill	Well	Attack Rate
Bologna	1	0	100%	8	12	40%	2.5
Hot Dog	1	1	50%	8	11	42.10%42%	1.191.2
Matambre	9	2	81.81%82%	0	10	0%	Undefined
Mate	4	4	50%	5	3	62.5%63%	0.790.8
Processed Ham	2	3	40%	7	9	43.75%44%	0.9
Sauce	7	2	77.77%78%	2	10	16.66%17%	4.584.6
Salami	1	1	50%	8	11	42.10%42%	1.191.2
Solid Ham	2	3	40%	7	9	43.75%44%	0.9

13) When relative risk = 1, exposure is not associated with disease

When relative risk< 1, exposure could be a protective factor

When relative risk> 1, exposure could be a risk factor for the disease

For bologna, hot dog, sauce & salami exposure to these items will 2.5 times, 1.2 times, 4.6 times & 1.2 times more likely to develop illness respectively. But mate, processed & solid ham consumption don't increase the disease developing chance. So, these items aren't contaminated. But there is chance that bologna, hot dog, sauce or salami might contaminated as consumption of these items increased the disease developing chance.

For further analysis we can do ² analysis test to determine the statistical significance of our observed data. From this test we can find if the observed relative risk could have occurred by chance alone.