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COMMUNITY DENTISTRY Cite this article: Khamis AH. Is Comparison of the Prevalence of Disease Appropriate as Health Indicator between two Populations? Stoma Edu J. 2014;1(2): 92-96. IS COMPARISON OF THE PREVALENCE OF DISEASE APPROPRIATE AS HEALTH INDICATOR BETWEEN TWO POPULATIONS? Amar Hassan Khamis1a*, Maanas Shah2b 1. Biostatistics and Research Unit, Hamdan Bin Mohammed College of Dental Medicine (HBMCDM), Dubai, United Arab Emirates 2. Department of Periodontology, Hamdan Bin Mohammed College of Dental Medicine (HBMCDM), Dubai, United Arab Emirates a. PhD, DEA, MSc, BSc, Associate Professor b. BDS, MSD, CAGS, Clinician Abstract Introduction: Prevalence is the most frequently used health indicator in order to assess the magnitude of a disease in a public health environment. It is a fraction that relates the number of screened disease cases divided by the total number of screened cases. When comparing two different study populations it is not possible to predict the proportions of old and new cases. This, when combined with variations in the health care delivery systems, makes the comparison of prevalence within two populations questionable. The objective of this study was to discuss the validity of the comparison of prevalence between two different populations. Methodology: Mathematical derivatives were presented to express the prevalence of a disease in a given population. Further fragmentation of the equations led to various probabilities pertaining to the number of old versus new cases that contributes to the prevalence of any existing disease. These calculations were applied to a theoretical example and final confirmation of its applicability was completed using various published scenarios from the Scientific Database. Results: The decomposition of the formula of prevalence to probabilities that measure new, old and normal case probabilities out of the screened individuals will lead to the fact that, not all the parts of these formula are comparable, due either to different settings, health systems or even to the time of exposure to a given impairment. Conclusion: The conclusion is that the prevalence of a disease between two different populations is unlikely to be comparable. Keyword: prevalence, prevalence comparison, health indicators, Dubai healthcare city. Introduction Received: 24 September 2014 Accepted: 06 October 2014 * Corresponding author: Associate Professor Amar Hassan Khamis, PhD, DEA, MSc, BSc Head of Biostatistics and Research Unit Hamdan Bin Mohammed College of Dental Medicine (HBMCDM) 34, Al Zahrawi Building Dubai, PO – 505097 United Arab Emirates Tel/Fax: +97144248787 e-mail: amar.hassan@dcdm.ac.ae 92 The recent definition of the word disease in the Oxford English dictionary is: a condition of the body or some part or organ of the body, in which its functions are disturbed or deranged; morbid physical conditions; a departure from state of health, especially when caused by structural change (1). This definition identifies a wide spectrum of the concept of the word disease from influenza to arthritis and from tuberculosis to cancer. In epidemiology and in biostatistics, despite the above-mentioned definition, a disease is considered as a dichotomous variable (yes or no) regardless of the status of the illness or the different states of the patient. The prevalence or prevalence proportion is an indicator that is frequently used in epidemiology to describe the number of people with a disease in a given population. The proportion of a population found to have a condition (typically a disease) is derived by STOMA.EDUJ (2014) 1 (2)