Introduction to Epidemiology 6th Edition by Ray M Merrill

Exercise 3

From Table 1, which malformations had the highest odds ratio? Which malformations had the lowest odds ratio?What is the significance of each?

Table 1 Odds Ratios for All Congenital Malformations and for Specific Malformations in Infants with Residential Proximity to Selected Hazardous Waste Sites, New York State, 1983–1984

Number of Cases‡	Congenital Malformation(s)	Odds Ratio†§
9,313	All malformations combined	1.12**
421	Nervous system	1.29*
2,730	Musculoskeletal system	1.16**
1,370	Integument system	1.32**
232	Oral clefts	1.15
429	Digestive system	0.89
245	Chromosomal anomalies	1.18
575	Syndromes||	1.15
4,003	Other (data too limited to infer associations with chemical exposure)	1.01

* p<0.05; ** p<0.01.

† Data from ICD-9, International Classification of Diseases, 9th revision

‡ The numbers of cases for the individual organ systems do not add up to the total number of cases for all defects combined because individuals may have had more than one defect.

§ Adjusted for maternal age, race, education, complications during pregnancy, parity, population density for county of residence, and gender of the child, by logistic regression.

|| Syndromes include all defects coded as “syndrome” in the New York State Congenital Malformations Registry, or any child with four or more defects.

Step 1 of 3

Odds Ratio measures the association with, and dependence of an outcome on the exposure to a test material. It is thus a means of quantification of the strength of presence and absence of a test substance on the perceived outcome.

It is calculated as the likelihood of occurrence of one condition, when a variable has already been applied to the likelihood of occurrence of the condition when a variable has not been applied.

For example, in the given case study, the condition is the incidence of a congenital malformation and the variable is the distance from the waste sites. It tells us about the odds of a child being born with congenital abnormalities given the distance from the hazard site plays a role.