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
Objectives Define and use Ratio Odds Rate Proportion Define and use Prevalence Incidence
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
Measurement of disease frequency Define ‘Disease’ Define population Define timeframe DISEASE FREQUENCY
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
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
Dichotomous variables Case –control Exposed –unexposed Dead –alive Ratio, proportion, rate
What, who is in the denominator ( 分母 )???? Ratio Proportion Rate
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
= 5 / 2 = 2.5 / 1 # beds per doctor 850 beds/10 doctors R = 85 beds for 1 doctor # participants per facilitator # inhabitants per latrine
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
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%
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
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
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
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
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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