Epidemiological investigations are classified into:
- Observational epidemiological studies
- Experimental epidemiological studies.
OBSERVATIONAL EPIDEMIOLOGICAL STUDIES
The observational epidemiological studies are categorized into two:
- Description studies
- Analytical studies
Descriptive Epidemiological Studies examines the health status of a community based on available data. For example, morbidity and mortality statistics obtained from hospital records are used to evaluate the health status of the population under study. This data gives the epidemiologist the particular type of disease that is common or most prevalent in such community. In descriptive epidemiological studies, the pattern of disease is described according to the persons involved with respect to their age, occupation, race, education and other characteristics including the place where the disease occurs (geographical and climatic factors). All these above mentioned factors are referred to as socio-demographic parameters; and they are important parameters that aid the epidemiologists in doing their main job of disease-tracking and prevention. The time the disease occurs during the year is also considered in order to know if there are seasonal variations or other cyclical changes which may be yearly or by other intervals.
Analytical Epidemiological Studies is divided into three areas:
- Cross-sectional studies
- Case-control studies
- Cohort studies.
Cross-sectional studies measure the prevalence of diseases at a particular time. This study is relatively easy, economic, and useful for studying exposures that are reasonable permanent features for individuals such as economic and socio-economic status. In a sudden outbreak of a disease, a cross-sectional study with measurement of potential causative factor is often the most convenient 1st step in an investigation of the cause of the outbreak. Data’s from this study are helpful in assessing the health care need of the population.
Case-control studies can also be called a retrospective study since the investigator is looking backward from the disease to a possible cause. This study begins with the selection of cases. Here, both the cases and the control participants in the study are chosen from the same population having the disease. The controls should be carefully chosen to be representatives of the population which generated the cases. It is a relatively easy and economical type of epidemiological study.
Cohort studies begin with a group of people known as cohort (i.e. people free of the disease under investigation) who are classified into subgroups with different exposures to a potential cause of a disease. For example, 100 people who are free from the disease can be selected and screened. These individuals don’t have the disease. This 100 people can be classified into 5 sub-groups as follows. 20A, 20B, 20C, 20D and 20E. They are then exposed to different concentration of the disease cause as thus:
20A 20B 20C 20D 20E
10L 5L 2L 1L 0.5L
NOTE: Laboratory animals can be used in carrying out this study. After this, they can now be examined for the development of the disease condition. Cohort study provides the best information about the causation of a disease and the most direct measurement of the risk of developing the disease. Cohort studies often require long follow up periods since there is often a long period after exposure before the occurrence of the disease.
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