Epidemiological studies occurrence

Epidemiology is the study of the patterns of disease occurrence in populations and of the factors affecting them. An epidemiological study identifies a new disease and its possible causative agents moreover, it identifies the population at high risk and presents factors increasing risk. 

There are two basic kinds of epidemiological studies, descriptive and analytical. The goal of the first is to describe the occurrence of disease in populations. Analytical studies identify and explain the cause of the disease. For instance, descriptive epidemiology may identify a new disease such as AIDS. Interpretation of descriptive results leads to analytical studies that examine the disease in more detail. Since epidemiology is the study of disease in populations, the proportion of affected individuals in a population is of basic importance. However, the epidemic pattern has varied from country to country. In the United States and the United Kingdom, 65% and 85%, respectively, of AIDS cases have... 

No epidemiological studies of hexachlorobutadiene are available. The occurrence of renal tumors after chronic oral exposure in rats suggests carcinogenicity may be an area of concern following occupational exposure to hexachlorobutadiene and long-term exposures from waste sites. 

Polybrominated Biphenyls. No epidemiological studies were located that provided evidence for an association between exposure to PBBs and the occurrence of cancer in humans, although one case report is available concerning gastrointestinal cancer in a Michigan dairy farmer with known exposure to PBBs and other chemicals. 

The results of a major epidemiological study of the geographical variations in the occurrence throughout China of a wide variety of different types of cancer have recently been published in the form of an atlas (146). One result of this survey was the revelation of a very high, but very localized, incidence of esophageal cancer in the Linxian valley of Henan province in northern China (146,147). Esophageal cancer also exhibits very high incidence in a number of other localities in both Asia and Africa (148), but the Chinese occurrence has so far attracted the most international attention. 

Epidemiological studies can be categorized into three major types (1) descriptive or studies based on routine data, (2) analytical observational studies in which the researcher observes the occurrence of disease in two groups already segregated by disease or exposure, and (3) experimental studies in which the researcher randomly assigns individuals to the exposure in question. 

After a study has been conducted, the data are analyzed to see whether an association is observed. This section briefly defines the two major measures of occurrence (incidence and prevalence) and discusses measures of associations in detail, focusing on the most common measures used in the epidemiological study designs described above, such as correlation coefficient, relative risk, and odds ratio. 

Nishimoto, Y., M. Yamakido, S. Ishioka, et al. 1988. Epidemiological studies of lung cancer in Japanese mustard gas workers. In Unusual Occurrences as Clues to Cancer Etiology, R.W. Miller et al., (eds). Japan. Sci. Soc. Press., Tokyo, pp. 95-101. 

In setting up an imaginary epidemiological study, 80 diabetics were selected from 497 diabetics, and 80 controls were selected from 9503 available controls. The occurrence of high or normal cholesterol in the small group (Table C.l) and big group (Table C.2) are shown. 

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