ABSTRACT
Nature is a great experimenter. Many changes occur naturally, requiring no human intervention. Some people are exposed to iodine-deficient water because of environmental conditions, and some women have low hemoglobin (Hb) levels because of their nutritional status. The study of such naturally occurring events can be invaluable in studying cause-effect relationship with conviction. Such a study can be based on records or on actual observations, or a combination of both. This type of study is generally categorized as an observational study, also sometimes referred to as an epidemiological study. Since there is no deliberate human intervention (such as a drug) in this setup, such studies carry little risk of harm to the subjects or the society, although they are invasive with regard to time and privacy of the respondents. An observational study is generally conducted for specific groups such as those with high disease prevalence; thus, extrapolation to the general population is not immediate. Many observational studies are done in a hospital setup rather than in communities.
