Measurements of disease.pptx by Dr. Amit gangwar

the various measures of morbidity and mortality such as prevalence, incidence, and mortality rate.
mapping and application of measures of diseases.
rate, ratio, and proportion which are the basic tools to measure the disease in a a population.
Relationship between prevalence and incidence rate.

1. Measurements of disease Amit Gangwar MVSc. scholar

2. Tool of measurements RATIO RATE PROPORTION

3. RATIO The value obtained by dividing one quantity by other - X/Y. relations between two quantities. Numerator is not a part of denominator. Ex. - Male : Female ratio WBC : RBC ratio

4. RATE expresses a change in one quantity (the numerator) with respect to another quantity (the denominator). ‘Time’ is included in the denominator. Ex. - Velocity (e.g., 10 m per second) is a rate.

5. Proportion Relation between two quantities. Numerator always parts of denominator. Ex. - prevalence, case fatality are proportions.

6. Measurements of morbidity Incidence Occurrence of new cases Prevalence Existence of all new & old cases.

7. Prevalence number of individuals having a disease at a particular point in time P = —————————————————————————————— nu mber of individuals in the population at risk at that point in time

8. Prevalence Point prevalence the amount of disease in a population at a particular point in time. Period prevalence number of cases that are known to have occurred during a specified period of time . Ex. - a year (annual prevalence).

9. INCIDENCE Two components: 1 - the number of new cases; 2 - the period of time over which the new cases occur.

10. Cumulative incidence Incidence Rate Proportion number of individuals that become diseased during a particular period ——————————————————————————————— number of healthy individuals in population at beginning of that period Rate number of new cases of disease that occur in a population during a particular period of time ————————————————————————————————— the sum, over all individuals, of the length of time at risk of developing disease

11. The relationship between prevalence and incidence rate P = I x D This means that a change in prevalence can be due to: 1 - a change in incidence rate. 2 - a change in the average duration of the disease. 3 - a change in both incidence rate and duration.

12. Attack rate Secondary attack rate describe the proportion of animals that develop the disease, when period of risk is brief. Rate at which disease is spreading. Expressed in %. proportion of cases of a transmissible disease that develop when contact with the primary case.

13. Mortality When the relevant outcome is death. Rather than new case of a specific disease.

14. Cumulative mortality estimated same as cumulative incidence. number of individuals that die during a particular period number of individuals in the population at the beginning of the period

15. Mortality rate Calculated same as incidence rate. number of deaths due to a disease that occur in a population particular period of time M= the sum over all individuals, of the length of time at risk of dying

16. Death rate The death rate is the total mortality rate for all diseases rather than one specific disease, in a population.

17. Case fatality rate The tendency for a condition to cause the death of affected animals in a specified time is the case fatality. proportion of diseased animals that die. number of deaths number of diseased animals CF=

18. Measures CRUDE Crude prevalence, incidence and mortality values are an expression of the amount of disease and deaths in a population as a whole . no account of the structure of the population affected. SPECIFIC describe disease occurrence in specific categories of the population. related to host such as age, sex, breed and method of husbandry, and, in man, occupation and socio-economic group. convey more information than crude measures on the pattern of disease. can indicate categories of animal that are particularly at risk of disease, and can provide evidence on its cause.

19. Measures Adjusted (standardised) Remove confounding of different age structures. Adjusting the crude values. reflect the values that would be expected if the potentially confounding characteristics were similarly distributed in the two study populations.

20. Mapping displaying the geographical (spatial) distribution of disease by drawing maps (cartography). recording of areas where diseases exist but also in investigating the mode and direction of transmission of infectious diseases.

21. POINT/DOT MAP illustrate outbreaks of disease in discrete locations, by circles, squares, dots or other symbols. Qualitative. Direction of spread of disease.

22. DISTRIBUTION MAP show the area over which disease occurs.

23. PROPORTIONAL CIRCLE MAP Morbidity and mortality can be depicted using circles whose area is proportional to the amount of disease or deaths. Shading is used to give the impression of spheres on a two-dimensional map.

24. CHOROPLETHIC MAP Greek: choros = ‘an area’, ‘a region’; plethos = ‘a throng’, ‘a crowd’, ‘the population. display quantitative information as discrete shaded units of areas. graded in intensity to represent the variability of the mapped data.

25. ISO PLETHIC MAP True boundaries between different values is depicted by joining all points of equal value by a line.

26. Why should we measure it? Describe the extent and nature of disease n community - assist in establishing priorities. Provide essential data for research. Starting point for etiological disease, help in PREVENTION. Monitoring and evaluation of disease control activities.

27. Thanks! Reference: Veterinary epidemiology, 3rd edition (Michael thrusfield)