ANTC67: Midterm Notes Chapter 2: Measuring Health and Disease Defining Health and Disease The most ambitious definition of health is that proposed by WHO in 1948: ^ZoZ]ZZ} }KoZZ] o7 mental, and social well- ]L2LL}KoZZL }]ZZ}]L]K]:_ This definition J criticized because of the difficulty in defining and measuring well-being. A specific cut-off point for an abnormal value is based on an operational definition and not on any absolute threshold. Diagnostic criteria are usually based on symptoms, signs, history, and test results. Diagnostic criteria may change quite rapidly as knowledge increases or diagnostic techniques improve; they also often change according to the context in which they are being used. Measuring Disease Frequency Several measures of disease frequency are based on the concepts of prevalence and incidence. ]K]}o}2]ZZZL} Z }Ko2KL}L]L]]}LKZ8[Z]L2>Z[ZDictionary or Epidemiology. Population at Risk An important factor in calculating measures of disease frequency is the correct estimate of the numbers of people under study. Ideally these numbers should only include people who are potentially susceptible to the diseases being studied. The people who are susceptible to a given disease are called the population at risk, and can be defined by demographic, geographic, or environmental factors. Incidence and Prevalence The incidence of disease represents the rate of occurrence of new cases arising in a given period in a specified populations, while prevalence is the frequency of existing cases in a defined population at given point in time. These are fundamentally different ways of measuring occurrence. If incident cases are not resolved, but continue over time, then they become existing (prevalent) cases. In this sense, prevalence = incidence x duration. Measuring prevalence and incidence involves the counting of cases in defined populations at risk. Reporting the number of cases without the reference to the population at risk can be used to five an impression of the overall magnitude of a health problem, or of short-term trends in a population. @ZK^ l_]Z}LZ]LZ} incidence during a disease outbreak in a narrowly-defined population over a short period of time. The attack rate can be calculated as the number o f people affected divided by the number exposed. A rate is calculated by dividing the number of the cases by the corresponding number of people in the population at risk and is expressed as cases per 10 people. Prevalence Prevalence (P) of a disease is calculated as follows: P= #of people with the diseasecondition at a specified time # of people in the population at risk at the specified time Data on the population at risk are not always available and in many studies the total population in the study area is used as an approximation. Prevalence is often expressed as cases per 100 (percentage), or per 1000 population. P ]ZZ^}]L}oL :_ ]ZZ}K]KZK} }LL]L}ZZ^]}}oL 7_ o oZZ}oLK} ZZL]K]L2 a specified period, divided by the population at risk midway through the period. ^]K]oo7^o]]KoL _]ZZ}oLK}Z}LZlL}L}ZZZ]ZZ}oZZ}K}Z] lives. Apart from age, several factors determine prevalence. In particular: www.notesolution.com

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