Measurements of morbidity and mortality

Measurements of morbidity and mortality
At the end of the session, the students shall be able to
List the basic measurements in epidemiology
Select an appropriate tools of measurement
Measure morbidity & mortality
Perform standardization of rates

1. Dr. Jayaramachandran S
Associate Professor
Dept. of Community Medicine
04.11.2019

2. Define Epidemiology
•Thestudyofthedistributionanddeterminantsofhealth-related
statesorevents
•inspecifiedpopulations
•andtheapplicationofthisstudytothecontrolofhealthproblems
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 2

3. Specific Learning Objectives
•At the end of the session, the students shall be able to
üList the basic measurements in epidemiology
üSelect an appropriate tools of measurement
üMeasure morbidity & mortality
üPerform standardization of rates
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 3

4. Basic measurements in
epidemiology
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 4

5. Basic measurements in epidemiology
•Measurements of mortality
•Measurements of morbidity
•Measurements of disability
•Measurements of natality
•Measurements of the presence, absence or distribution of the
characteristics or attributes of the disease
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 5

6. Basic measurements in epidemiology
•Measurements of the presence, absence or distribution of the
environmental and other factors suspected of causing the disease.
•Measurements of the medical needs, health care facilities, utilization
of health services and other factors suspected of causing the disease.
•Measurements of demographic variables.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 6

7. Tools of measurement
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 7

8. Tools of measurement
1.Rates
2.Ratios
3.Proportions
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 8

9. 1.Rate
•A rate measures the occurrence of some particular event (
development of disease or the occurrence of death) in a population
during given time period.
•CDR=No.ofdeathsinoneyear
Midyearpopula9on×1000
•Consists : Numerator, denominator, time factor and multiplier
•e.g.. CBR, CDR.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 9

10. Various categories of rates
a)Cruderates:Thesearetheactualobservedratessuchasthebirth
anddeathrates.(unstandardizedrates)
b)Specificrates:Thesearetheactualobservedratesduetospecific
causes(e.g..tuberculosis);oroccurringinspecificgroups(e.g.,age-
sexgroups)orduringspecifictimeperiods(e.g.,annual,monthlyor
weeklyrates).
c)Standardizedrates:Theseareobtainedbydirectorindirectmethod
ofstandardizationoradjustment,e.g.AgeandSexstandardized
rates.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 10

11. 2.Ratio
•It expresses a relation between two random quantities.
•!∶#or $
%
•E.g. Sex ratio, child-woman ratio, doctor-population ratio.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 11

12. 3.Proportion
•A proportion is a ratio which indicates the relation in magnitude of a
part of the whole.
•The numerator is always included in denominator.
•The proportion is usually expressed in percentage.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 12

13. Measurements of mortality
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 13

14. Crude death rate
•CDRisthenumberofdeaths(fromallcauses)per1000estimatedmidyearpopulationinoneyear,inagivenplace.
•CDR=No.ofdeathsinoneyear
Midyearpopula>on×1000
•LimitationofCDRisexposedwhenwecompareage-specificdeathratesb/wtwopopulations.
•MajordisadvantageofCDRisthattheylackcomparabilityforcommunitiespopulationsthatdifferbyage,sex,race,etc.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 14

15. Specific death rate (SDR)
•SDR=Deathduetospeci0iccause
Midyearpopula+on×1000
•Useful when planning to find out etiology :
•Cause or disease specific e.g. TB, Cancer, etc.
•Related to specific groups-age specific, sex specific, etc.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 15

16. Specific death rate
•Advantages: It helps us to identify particular groups or groups at risk
for preventive action. They permit comparisons b/w different causes
with in same population
•Disadvantages: mainly used in developed countries where they have
civil registration system.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 16

17. 20/11/19Measurement of Mortality & Morbidity -Dr. JRC 17

18. Case fatality rate (CFR)
•CFR=Totalno.ofdeathsduetopar0culardisease
Totalno.ofcasesduetothesamedisease×100
•It represents the Ratio of death to cases
•Virulence of organism & killing power of a disease
•Useful in acute infectious diseases e.g. cholera, measles
•Time interval is not specified
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 18

19. Proportional mortality rate (ratio)
•No of deaths due to a particular cause or in a specific age group per 100 or 1000 deaths”.
a) Proportional mortality of a specific disease
=No.ofdeathsfromthespecificdiseaseinayear
Totaldeathsfromallcausesinthatyear×100
b) Under 5 proportionate mortality rate
=No.ofdeathsunder5yrsofageinagivenyear
Totalno.ofdeathsduringthesameperiod×100
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 19

20. Proportional mortality rate (ratio)
•Proportional mortality rates are usually used for broad disease group
and for specific disease of major public health importance e.g.,
cancer, CHD
•It is used when population data is not available
•Depends upon only two variables, which differ. So, it cannot be used
for comparison b/w population groups or different time periods.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 20

21. Survival rate (SR)
•SR=Totalno.ofpa*entsaliveoveraperiod
Totalno.ofpa*entsdiagnosedortreated×100
•Itisthepopulationofsurvivorsinagroupstudiedandfollowedovera
period.e.g.for5yearsperiod
•Helpsindescribingprognosisincertaindisease
•Canbeusedasayardstickfortheassessmentofstandardsof
therapy.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 21

22. Adjusted or standardized rates
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 22

23. Adjusted or standardized rates
•It’smajoradvantageisabletocomparedeathratesoftwo
populationswithdifferentage-composition.
•Thisisbecauseratesareonlycomparableifthepopulationsupon
whichtheyarebasedarecomparable.
•Itremovestheconfoundingeffectofdifferentagestructuresand
yieldsasinglestandardizedoradjustedratebywhichwecan
comparemortalitydirectly
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 23

24. Two methods of standardization
•Direct standardization
•Indirect standardization
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 24

25. Direct standardization
•First a “ standard population” is selected (nos. in each group are
known)
•Secondly age specific rates are applied to standard population whose
crude death rate is intended to be adjusted or standardized
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 25

26. Indirect standardization
•Standardized Mortality Ratio (SMR) (expressed as percentage)
•SMR=Observeddeaths
Expecteddeaths×100
•Applications of SMR:SMR compares the mortality in a study group
(e.g.. an occupational group) with the mortality that the occupational
group would have had if they had experienced national mortality
rates.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 26

27. Indirect standardization
•IfSMRisgreaterthan100,thentheoccupationwouldappeartocarry
agreatermortalityriskthanthatofthewholepopulation.
•IfSMRislessthan100,thentheoccupationrisksofmortalitywould
seemtobeproportionatelylessthanthatforthewholepopulation.
•TheSMRisbetterthandirectstandardizationbecauseitpermits
adjustmentforageandotherfactors.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 27

28. Measurements of morbidity
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 28

29. Measurements of morbidity
•Morbidity is defined as “any departure, subjective or objective, from
a state of physiological well-being”.
•Morbidity rates/ratios measured by
a)Frequency of disease: incidence and prevalence
b)Duration of illness: days, months and years
c)Severity of illness: case fatality rates
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 29

30. Importance of morbidity data
•Toknowextentandnatureofthediseaseloadincommunityand
helpinformingpriorities.
•Providemorecomprehensiveandaccurateandclinicallyrelevant
informationonpatientcharacteristics–essentialforbasicresearch.
•Startingpointofetiologicalstudiesandplayscrucialroleindisease
population.
•Neededformonitoringandevaluationofdiseasecontrolactivities.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 30

31. Incidence
•Incidence
=No.ofnewcasesofspecificdiseaseduringagiven3meperiod
Popula3onatriskduringthatperiod×1000
•Newspellsorepisodesofdiseaseinagivenpopulationinthegiven
duration
•Usuallyrestrictedtoacuteconditions
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 31

32. Special incidence rates
•Attack rate (case rate), Secondary attack rate, Hospital admission rate
•Attack rate: An attack rate is an incidence rate (usually expressed as a
per cent), used only when the population is exposed to risk for a
limited period of time such as during an epidemic.
•It reflects the extent of the epidemic.
=NumberofnewcasesofaspecifieddiseaseduringaspecifiedCmeinterva
TotalpopulaConatriskduringthesameinterval×100
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 32

33. Secondary attack rate
•SAR=
Noofexposedpersonsdevelopingdiseasewithintherangeoftheincuba6on
Totalnoexposed/“suscep6ble”contact×100
•Primary case is excluded from both numerator and denominator.
•Limitation:
•Useful only for disease with short incubation period
•Not possible to identify susceptible cases
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 33

34. Uses of incidence rate
•To control disease, and
•For research into aetiology and pathogenesis, distribution of diseases,
and efficacy of preventive and therapeutic measures.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 34

35. Cumulative incidence
•CI=
No.ofpeoplewhogetadiseaseduringaspecifiedperiod
No.ofpeoplefreeofthediseaseinthepopula5onatriskatthebeginningoftheperiod×1000
•Cumulativeincidenceisasimplermeasureoftheoccurrenceofadiseaseorhealthstatus.
•Unlikeincidence,itmeasuresthedenominatoronlyatthebeginningofastudy.
•Inastatisticalsense,thecumulativeincidenceistheprobabilitythatindividualsinthepopulationgetthediseaseduringthespecifiedperiod.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 35

36. Cumulative incidence
•The period can be of any length but is usually several years, or even
the whole lifetime.
•The cumulative incidence rate therefore is similar to the “risk of
death” concept used in life-table calculations.
•The simplicity of cumulative incidence rates makes them useful when
communicating health information to the general public.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 36

37. Prevalence
•The term "disease prevalence" refers specifically to all current cases
(old and new) existing at a given point in time, or over a period of
time in a given population.
•Prevalence is a ratio but expressed as a rate
•Two types
•Point prevalence
•Period prevalence
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 37

38. Prevalence
•Pointprevalence=
Noofallcurrentcases(old+new)atonepointof6meinadefinedpopula6on
Es6matedpopula6onatthesamepointin6me×100
•Periodprevalence=
No.ofexis6ngcases(old+new)duringagivenperiodof6meinterval
Es6matedmid−intervalpopula6onatrisk×100
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 38

39. Relationship between prevalence & incidence
•Prevalence = Incidence x Duration.
•(if population is stable and incidence and duration are unchanging)
•Longer the duration: greater is the prevalence rate e.g. TB
•Acute disease: short duration and rapid recovery. So prevalence is less
than incidence.
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 39

40. 20/11/19Measurement of Mortality & Morbidity -Dr. JRC 40

41. 20/11/19Measurement of Mortality & Morbidity -Dr. JRC 41

42. Uses of prevalence
•Estimating magnitude of health/ disease problems in the community
•Identify potential risk populations
•Useful for administrative and planning purposes
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 42

43. Summary
•List the basic measurements in epidemiology
•Select an appropriate tools of measurement
•Measure morbidity & mortality
•Perform standardization of rates
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 43

44. Any Questions???
20/11/19Measurement of Mortality & Morbidity -Dr. JRC 44