DETERMINATION OF RISK FACTORS

Conditions suspected of contributing to the development of a disease are called risk factors. They may be inherent to the person (high blood pressure or overweight) or external (smoking or drinking alcohol). There are different types of studies used to determine risk factors, including cross-sectional studies, case-control studies, and cohort studies. Cross-sectional studies use the simultaneous collection of information necessary for classification of exposure and outcome status. They can be used to compare the preva­lence of a disease in those with the factor (or exposure) with the prevalence of a disease in those who are un-exposed to the factor, such as the prevalence of coronary heart disease in smokers and nonsmokers. Case-control studies are designed to compare persons known to have the outcome of interest (cases) and those known not to have

31.4%

.1%

30 35

Heart Disease Cancer

Stroke

Chronic Obstructive Pulmonary Disease

Unintentional Injuries

Pneumonia/Influenza

Diabetes

Suicide

Kidney Disease

Chronic Liver Disease and Cirrhosis

10 Leading Causes of Death, 1997

23.3%

10 15 20 25 Percent of all deaths

	10	Leading Causes of Death, 1900
Pneumonia			11.8%
Tuberculosis			11.3%
			3%
Diarrhea and enteritis		8
Heart Disease		|] 6.2%
Liver Disease		1 5.2%
Injuries		4.2%
Cancer		3.7%
Senility		2.9%
Diphtheria	j] 2.3%
С	)	5 10 15 20 25 30 3
		Percent of all deaths

 

the outcome of interest (control). Information on expo­sures or characteristics of interest is then collected from persons in both groups. For example, the characteristics of maternal alcohol consumption in infants born with fetal alcohol syndrome (cases) can be compared with those in infants born without the syndrome (control). A cohort is a group of persons who were born at approximately the same time or share some characteristics of interest. Persons enrolled in a cohort study (also called a longitudinal study) are followed over a period to observe some health outcome. A cohort may consist of a single group of persons chosen because they have or have not been exposed to suspected risk factors; two groups specifically selected because one has been exposed and the other has not; or a single ex­posed group in which the results are compared with the general population. The Framingham Study, which exam­ined the characteristics of people who would later experi­ence coronary heart disease, and the Nurses' Health Study, which initially explored the relationship between oral contraceptives and breast cancer, are two well-known co­hort studies.