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Measures of Morbidity

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www.cdc.gov/mmwr

Morbidity and Mortality Weekly Reports

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Terms Related to Morbidity

MorbidityThe extent of illness, in ury or disability in adefined population

!ncidence of a disease "!ncidence rate#The number of new cases of a disease thatoccur during a specified time period"numerator# in a population at risk fordeveloping the disease "denominator#

$revalence of a disease "$revalence rate#The number of total cases of disease presentat a particular time "numerator# in a specificpopulation "denominator#

RiskThe likelihood that an individual will contract a

disease

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%haracteristics

R!&' $R()*+( %( ! %!-( %(R*T(

$robability ofdisease

of pop. withthe disease

Rapidity ofdisease

occurrence

o units o units %ases perperson time

ewlydiagnosed (xisting ewlydiagnosed

0%umulativeincidence1

0!ncidencedensity1

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$roblems with umerators Who has the disease2 Who to include in numerator2 !nterview errors

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$roblems with 3ospital -ata

&elective "many reasons# -ata may be unavailable, etc

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!ncidence

The two forms of incidence are4 %umulative incidence

"risk of disease

measures the proportion ofpersons who develop a disease in aknown span of time

!ncidence rate "rate of disease measures the rate of new diseaseoccurrence over time

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!ncidence per 5666

Whats wrong with this formula?

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!ncidence Rate

Measures the rapidity with which newlydiagnosed cases of the disease of interestdevelop

observe a population count 7 of new cases measure net time

individuals in population at risk of developing disease

person time person years patient days

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!ncidence Rate "*ttack Rate# "cont.#

%an be used for specific exposures *lso used for multiple exposures 8ther terms4

primary casesecondary attack

secondary cases

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$rinciples of !ncidence Rate

(stimate probability !ncidence kinetics &easonal variation $lace

$erson

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*ttack rates

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!ncidence and *ttack Rates

$rimary *ttack rates

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!ncidence and *ttack rates"cont9d#

&econdary *ttack rates

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!ncidence Rates

8&3*

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$revalence Measure of the number "or proportion# of

cases in a given population What is the difference between prevalence

and incidence 2

$revalence a slice thru a population at agiven point in time that determines who hasthe disease and who does not, while !ncidenceonly looks at new cases

!n steady state situation "no change in rateor net population#

$revalence : !ncidence ; -uration of disease

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$revalence

$oint prevalence point in time $eriod prevalence during a defined

range of time

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%omparative

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%omparative

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$revalence Rates

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$revalence Rates

$oint

$eriod

"cont9d#

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Rates of Morbidity=reast %ancer !ncidence in White Women and

-istribution by *ge

Note change in slope menopause??

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%ase -istribution&pot Map of Residence -istribution ofRheumatic ?65>?@

5>AA5>B5

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&ources of Morbidity &tatistics

%linical and hospital Managed care Registries

)ital statistics &urveys -isease reporting

!nsurance and pre paid med. care plans *bsenteeism records

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