In a descriptive health study, the researcher collects information to better understand if there may be a possible association between an exposure and health outcome. The findings of this study often provide the first evidence that there may be a potential health hazard due to an exposure. Below are some of the different types of descriptive health studies that can be conducted in a community.

type of study Health Outcome Data Reviews
(review of health statistics)
questions that
may be answered		 was there an excess of disease in this defined geographical area during a certain period of time?
target population people who developed a specific disease within a defined population
information and
resources needed		 a registry or database for the disease being investigated
defined time period in which disease is expected to occur
statistician or epidemiologist to evaluate the expected number of cases versus actual number of cases
limitations diseases might not be reported to the registry
diseases are not always recorded correctly
not all diseases are recorded in a registry
type of study Case Reports
(document an unusual pattern among a specific disease case or group of cases)
questions that
may be answered		 is this an unusual occurrence of disease that suggests a previously unknown link between exposure and disease?
target population people who have an unusual disease that seemed to have developed a after a unique exposure
information and
resources needed		 medical records, interviews, biomedical testing, some medical information on people with a specific, often unusual disease
often useful to have a medical doctor or epidemiologist
limitations useful for discovering possible new links between exposures and diseases, but not for showing cause and effect
often case reports are not planned research studies but are due to careful observations from a medical doctor or epidemiologist
type of study Case Series
(investigate a specific disease among a group of cases)
questions that
may be answered		 what are some possible common characteristics shared by people with a certain disease?
target population people who have the same disease
information and
resources needed		 medical records, interviews, biomedical testing, some medical information on people with a specific disease
often useful to have a medical doctor or epidemiologist
limitations useful for creating a list of possible risk factors, but not for showing cause and effect
Health Outcome Data Reviews
A health outcome data review involves reviewing the number of actual disease cases that occurred in a community exposed to a contaminant, and comparing it to the number of disease cases expected in that community. The number of disease cases expected is based on standard disease rates found in a national or state registry. Standard rates are assumed to represent the occurrence of a specific disease in the absence of exposure to an environmental contaminant.

For example, in California and other areas in which a cancer registry exists, we can look at numbers of cancer cases for a specific geographical area. This can be helpful in determining if the number of cancer cases in a specific area is lower or higher than what is expected.

This technique has limitations in what we can conclude from its results. The registry only has information about where someone lived at the time of their diagnosis. Because people move around frequently, we do not know if the people with cancer in the registry had actually lived in that location for very long. This makes it difficult to determine if their cancer was in fact related to something in the environment in which they lived.

Another important limitation is that not all diseases have registries. For example, in California, data currently registered includes births, deaths, cancer and selected communicable diseases (HIV/AIDS, tuberculosis, chlamydia, gonorrhea). Many diseases do not have to be reported and are not recorded in a state registry. Therefore, it is not always possible to conduct a health outcome data review.

Case Reports
Case reports are descriptions of an unusual disease occurrence among an individual or group of people that seemed to have developed after a unique exposure. The disease occurrence often includes an uncommon set of signs and symptoms. The unique exposure may be a new, experimental medication or a particular chemical.

For example, doctors noticed that several young, non-smoking workers were developing severe lung disease. The disease was so severe that many needed lung transplants. Doctors discovered that these workers had inhaled butter flavoring in microwave popcorn through their jobs. These doctors wrote case reports that resulted in an investigation by the National Institute for Occupational Health and Safety.

Case Series
While a case report often documents the initial occurrence of a disease and its possible link to exposure, a case series looks at multiple occurrences of the disease. Case series include the collection and evaluation of medical records and information for an ill person or a group of people with the same health outcome.

The doctor or epidemiologist uses medical records, interviews, or biomedical testing to learn more about the common characteristics of people who have the same health outcome. These characteristics may help identify a potential factor that led to the development of the health outcome, such as genetic susceptibility or exposure to a certain contaminant.