Measures of Disease Occurrance.pptx - measures of disease occurrence Yan He Capital Medical University Objectives Define and use Ratio Odds Rate

Measures of Disease Occurrance.pptx - measures of disease...

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measures of disease occurrence Yan He Capital Medical University
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Objectives Define and use Ratio Odds Rate Proportion Define and use Prevalence Incidence
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Fundamental question Is a subject (individual, group, herd, region, country) diseased (abnormal, affected) or not diseased (normal, unaffected) ? Most health statistics and epidemiological research are based on counting of cases
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Measurement of disease frequency Define ‘Disease’ Define population Define timeframe DISEASE FREQUENCY
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Case definition The set of criteria that differentiate normality from abnormality Most important step in epidemiology Clinical/laboratory/epidemiological May need revision as knowledge advances
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Defining the population Usually easier than case definition Equally important Unit of interest (person, group, nation) Defined geographically or by other specific criteria Target, study and sample populations
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Dichotomous variables Case –control Exposed –unexposed Dead –alive Ratio, proportion, rate
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What, who is in the denominator ( 分母 )???? Ratio Proportion Rate
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Ratio (比率) The quotient (商) of 2 numbers Numerator (分子) NOT necessarily INCLUDED in the denominator (分母) Allows to compare quantities (量) of different nature
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= 5 / 2 = 2.5 / 1 # beds per doctor 850 beds/10 doctors R = 85 beds for 1 doctor # participants per facilitator # inhabitants per latrine
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Proportion (比率) The quotient of 2 numbers Numerator (分子) NECESSARELY INCLUDED (分母) in the denominator Quantities have to be of same nature Proportion always ranges between 0 and 1 Percentage = proportion x 100
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2 --- = 0.5 = 50% 4 Persons in denominator reflect population from which cases (numerator) arose Proportion of German EPIET in 8 first cohorts 101 trainees, 9 German Proportion of German trainees = 0.09 Percentage of German trainees = 9%
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Rate The quotient of 2 numbers Speed of occurrence of an event over time Observed in 1998 Numerator number EVENTS observed for a given time
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2 ----- = 0.02 / year 100 Observed in 1998 Numerator number EVENTS observed for a given time Denominator population in which the events may occur ( population at risk ) - includes time
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Rate, Example Mortality rate of tetanus in France in 1995 Tetanus deaths: 17 Population in 1995: 58 million Mortality rate = Rate may be expressed in any power of 10 100, 1,000, 10,00, 100,000 0.029/100,000/year
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Measures of disease occurence Epidemiology : «  Study of the occurrence of illness  » Two types of measures : Prevalence Measures population disease status Incidence Assess frequency of disease onset Cumulative incidence or incidence proportion Incidence density or incidence rate
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incidence Incidence quantifies the number of new evens or cases of disease that develop in a population of individuals at risk during a special time interval.
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  • Spring '16
  • Epidemiology, Tobacco smoking, Causality, Medical statistics

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