Observational epidemiological studies are non-experimental epidemiological investigations that involves no intervention by the researcher (in this case the epidemiologist) other than carrying out medical and laboratory examinations and probably asking questions about the issue at hand. In this type of epidemiological study, nature is allowed to take its full course while the researcher only observes passively and measures some disease parameters (factors) but does not interfere. This type of study design allows one or more groups of subjects and their disease characteristics to be observed and described/analyzed. Observational epidemiological study investigates the cause, prevention and possibly the treatment of a disease outbreak. In observational study, the investigator is merely an observer who only records potential factors of the disease/infection and the outcome of the poor health of the community. He/she notes the number of exposed and unexposed individuals in the population and, also the proportion of persons who has developed or has not at all developed the expected disease outcome.
Observational studies provide data that explains the occurrence of disease and determinants of disease evolution in order to control the disease and plan the prospects of the population’s health care needs. Though observational epidemiological studies can be used to study the effects of a broader range of exposures to a disease/infection, it is still not without some limitations. Firstly, investigators who opt to use observational study designs have limited or no complete control over some alarming factors bothering on their study – as they only observe passively and allow nature to take its course. Secondly, the observed group in the investigation may differ in many other features other than that being studied. Observational study does not require any ethical consideration before it can be undertaken, and it takes advantage from the fact that individuals of a population/community are exposed to certain disease/infection following their personal habits (e.g. smoking, drinking), occupation, time and place of work among other factors. The relationship between a given exposure or risk factor for the acquisition of a disease/infection in a community/population, and its outcome can be studied in several ways. Observational epidemiological studies therefore can be either descriptive or analytical study design.
Descriptive epidemiological studies look at the frequency and distribution of a disease/infection within a population. It is usually the first step in any epidemiological survey and, it only describes the occurrence or outcome of a disease in a community/population. In a descriptive study, the general features of an infection in a population are typically described in relation to the time, place and person getting the disease and, in what rate or frequency the disease is occurring in the community under investigation. Place, time, and person are very important epidemiological variables that are looked out for in any descriptive epidemiological study and, which allows a public health worker or an epidemiologist to decipher by descriptive approach the extent of a disease being investigated in a population, know the number of individuals that are easily contaminated, and most of all the proportion of persons at risk of acquiring the disease/infection. Such knowledge help health policy makers to effectively plan interventional measures and other preventive, treatment and educational programs that will help to reduce the scourge of the prevailing disease within the community.
Descriptive epidemiological studies are deficient and limited in their usage in that they only look at the features of some group of people with a given disease/infection without actually comparing them with some other reference or non-affected individuals of the population. Epidemiological studies that are descriptive in design are usually used for the formulation and development of hypothesis that are normally tested with a more detailed study (e.g. analytical epidemiological study).
Descriptive epidemiological study may include:
- Case reports
- Cross-sectional (Prevalence) studies
- Case series
- Ecological (Correlational) studies
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