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Measurements in epidemiology

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Measurements in epidemiology

  1. 1. Disease Disease frequency. frequency. Distribution Distribution. determinants. Determinants.
  2. 2.  Mortality.  Morbidity.  Disability.  Presence & absence or distribution of..  Medical needs.  Utilization of health services.  Demographic variables.
  3. 3. Rate Ratio Proportion
  4. 4.  Measures the occurrence of an event or disease in a given population during a given period (one Year). (Birth rate, growth rate, accident rate)  Usually expressed per 100 or per1000 population.  It has a time dimension, whereas a PROPORTION does not.
  5. 5.  A fraction is made up of 2 numbers.  The top number is called the NUMERATOR  and the bottom number is called the DENOMINATOR.  In the fraction ¾ the 3 is the numerator and the 4 is the denominator.
  6. 6. No of death in one year  Death rate= -------------------- X 1000 Total mid year population Numerator Denominator. Time specification Multiplier (Numerator is part of denominator )
  7. 7.  The value obtained by dividing one quantity by another- X/Y.  Male to female ratio.  A ratio often compares two rates, death rates for women and men at a given age.
  8. 8.  Ratio also expresses relation of size between the two quantities.  Numerator is not part of Denominator.  Expressed as X / Y. Doctor : Population ratio. Male : Female ratio. WBC : RBC ratio
  9. 9.  A part/share or number considered in comparative relation to a whole.  "the proportion of greenhouse gases in the atmosphere is rising”  Usually expressed as a percentage %
  10. 10.  This is also relation /magnitude between two quantities, And numerator is always part of denominator.  And expressed as percentage -Proportion of female students . -Proportion of anemic mothers (60% mothers are anemic)
  11. 11. Incidence Occurrence of new cases • Prevalence Existence of all new & old cases.
  12. 12.  Prevalence:- how many people in a population currently have the disease (Photograph)  Incidence:- how many people are diagnosed each year (Film)
  13. 13. Cure rate
  14. 14. New cases
  15. 15. • The rate at which acute disease is spreading -- used during epidemics & expressed in %. Attack rate • % of exposed persons developing disease after primary case exposure Secondary attack rate
  16. 16. •Prevalence at any given point of time. • 4% TB cases on 1st April Point prevalence •Prevalence at a given period of time. •Period will be 1year. Period prevalence
  17. 17.  Longer duration of the disease.  Prolongation of life, with treatment.  If incidence increases.  Immigration of new cases.  Better reporting of cases.  Emigration of healthy people.
  18. 18. Longer duration of disease Incidence increases. Prolongation of life without cure. 20
  19. 19.  Shorter duration of diseases.  Improved cure rate.  Incidence decreases.  Emigration of new cases.  Under reporting of cases.  Immigration of healthy people.
  20. 20. Improved cure rate. Short duration of disease. Incidence decreases
  21. 21.  Crude Death Rate.  Specific death rate.  Case fatality rate.  Proportional mortality rate.  Survival rate.  Standardized death rate.
  22. 22.  Number of deaths from all causes, per 1000 estimated mid year population in one year in a given place. No deaths during one year CDR = _________________________ X 1000 Mid year population
  23. 23.  Cause Specific death rate like disease death rate, Road accident…  Age specific-IMR, Child Mortality rate  Sex specific death rate – MMR/female  Period specific death rate–Death in May
  24. 24.  Percentage of particular cases dying during particular disease epidemic.  Killing power of disease particularly acute diseases No of deaths due to cholera  CFR= ----------------------- X 100 Total No of cholera cases
  25. 25.  Proportion or % of deaths due to particular cause out of total deaths.  It measures the disease burden.  Under 5, No of deaths below 5 years proportional = -------------------- X 100 mortality rate Total No all of deaths
  26. 26.  Percentage of the treated patients remaining alive at the end of 5 years treatment.  Yard stick for assessing the standard of therapy in cancer.  Survival pts alive at the end of 5 yrs Rate = ---------------------- X 100 Total No of pts treated
  27. 27.  CDR can not be useful for comparison.  Death rate need to be standardized for comparisons.  Standardization can be done by- :adjusting death rate age wise, :also can be done sex/race wise

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