CHS - Essentials - Analytical Health Studies

While descriptive health studies can first alert scientists and community members that an exposure may be a health hazard, analytical health studies can provide further evidence of an association between exposure and disease. Analytical health studies in environmental epidemiology involve comparing disease rates in a group of people with exposure to a contaminant with disease rates in a group of people without exposure. Below are some of the different types of analytical health studies that can be conducted in a community.

type of study	Cross-Sectional Study (study of health and exposure at one point in time)
questions that may be answered	at this specific point in time, does it appear that this exposure is related to this health outcome? does the data suggest that this exposure may be a risk factor for developing the health outcome?
target population	defined population that you are interested in at a specific point in time
information and resources needed	method to measure the exposure record of disease occurrence environmental scientist to measure the exposure statistician or epidemiologist to analyze data
limitations	cannot determine if the exposure occurred before or after the disease developed in a person
type of study	Cohort Study (study of people with and without exposure over a period of time)
questions that may be answered	are people with this exposure more likely to develop this health outcome? is this exposure associated with this health outcome? is there evidence of cause and effect relationship between exposure and health outcome?
target population	people who were exposed to the contaminant people who were not exposed to the contaminant
information and resources needed	method to measure exposure record of disease occurrence environmental scientist to measure exposure statistician or epidemiologist to analyze data
limitations	may be difficult to correctly determine if a person develops this health outcome or not is often expensive to do and can take several years to conduct may be difficult to get sufficient study power
type of study	Case-Control Study (study of people with and without a disease over a period of time)
questions that may be answered	are people with this health outcome more likely to have been exposed? is this exposure associated with this health outcome? is there evidence of cause and effect relationship between exposure and health outcome?
target population	people who have the health outcome people who do not have the health outcome
information and resources needed	method to measure exposure record of disease occurrence environmental scientist to measure exposure statistician or epidemiologist to analyze data
limitations	may be difficult to correctly determine if a person was exposed to a contaminant or not is often expensive to do and can take several years to conduct may be difficult to get sufficient study power

Cross-Sectional Study

The researcher identifies a specific population. Then the researcher finds out whether each individual has a health outcome, and whether each individual was exposed to a certain hazard. In a cross-sectional study, an individual's exposure and health outcome status are examined at the same time.

An important limitation of this type of study is that it cannot determine what came first: the exposure or the health outcome. Therefore, this type of study can only suggest that there might be a possible connection between a hazard and a health outcome. A cohort study or case-control study can give you stronger evidence of this connection.

Cohort Study

The researcher looks at a group of people exposed to a certain hazard, and a group of people not exposed to the hazard. The number of people who develop the disease in these two groups is compared after a period of time. If the exposure is associated with the disease, then the group of people exposed to a certain hazard would have a higher percentage of people with the disease than the group of people not exposed to the hazard.

Case-Control Study

The researcher identifies a group of cases (people with a specific health outcome) and a group of controls (people without that specific health outcome). Then the researcher examines the cases and the controls separately, to see how many people in each group were exposed to a particular contaminant in the past. If the exposure is associated with the disease, then the cases would have a higher percentage of people exposed to the hazard than the controls.