1. Measures of Population and Vital Statistics

2. The objectives of measuring population, vital statistics and morbidity in the field of preventive medicine and public health are:

3. i. To calculate indices that measure levels of health and morbidity in a population.
ii. To compare natality. mortality or morbidity of different places, times, communities and professions. Com­parison may also be useful as per age, sex and different socio-economic conditions.
iii. To monitor the progress made in the health and family welfare programmes.
iv. To fix up "priorities" in adoption of future health measures based on feed-back on the nature of the problem.
V. To determine the expectation or longevity of life at birth or at any particular age.
To determine the chances of survival or the proportion or percentage of survivors at any specific age following an intervention or therapy in a particular disease.
e.g. .. cancer.

4. MEASURES OF POPULATION
Mid-year Population (Mean population, population on July1st).Used in calculation of rates.
The main source of population and its socio-demographical composition is census, carried out every 10 years.
It forms the basis for projecting population data for any year.

5. To calculate indices of health, the total events in a particular year such as births, deaths and morbidity of a defined geographical area form the numerator and the population exposed in that year on first July or mid-year population as popularly called, forms the denominator.
This ratio may be multiplied by 100, 1000, 100,000, etc., to get the figure of convenient magnitude for easy comparison.

6. There are three methods for calculation of mid-year population:   
 A. Natural Increase Method   
Natural increase implies the difference between increase in population due to births and immigration and decrease due to deaths and emigration over a period of time say 1 year or 6 years.
This can be added to the previous census population to get the mid-year population of a particular year up to which the net increase has been calculated.   

7. B. Arithmetical Progression or AP Method   
Here it is assumed that there is equal increase each year and average increase per year is calculated in the intercensal period of 10 years such as between 1981 and  Population of any year or up to a particular month == last Census population + period in years and months after the last census month and year x yearly increase.  

8. C. Geometrical Progression or GP Method
It is easy to calculate with the help of log tables.

9. MEASURES OF VITAL STATISTICS
Absolute number of vital events such as births and deaths are converted into rates and ratios for comparison of vital statistics from place to place or year to year.

10. Rate
Rate is a proportion with a defined denominator termed as population.
The numerator is occurrence of an event which is counted in the same population. Multiply by 100, 1000, 10,000, etc. as per magnification desired.
When occurrence of an eventes rare such as cancer. multiply by
Rate differs from proportion in the matter of time. No time factor is involved in the proportion. The rate is a measure of the speed at which new events are occurring in a community. The rates, in general, are of two types crude and specific.

11. i. Crude Rate- Crude rates are general rates calculated without paying regard to specific sections of the population. They measure the proportion between total events and the total population over a period of time.
Crude rate
Total number of events that occurred in a given geographical area during a given year__________ x 1000
Mid-year population of the geographIcal areas for the same period

12. Specific Rate This rate is for specific group of the population such as for a particular age, sex, marital status, occupation, etc.
Number of events which occurred among a specific group of the population of a given geographic area during a given year x 1000
Mid-year population of the specific group of the population in the same geographic area during the same period

13. Measures of Fertility.
Crude Birth Rate .
It is the most commonly used composite index of increase in population by natality or child birth.
The formula is: Annual crude live birth rate
Number of live births which occurred among the population of a given geographic area during a given year x 1000
Mid- year population· of the same geographic area during the same year
Note-'Llve' is distinct from 'total births' which include still births too.

14. Fertility Rate
This rate is related to women in the reproductive period hence it is better to measure the fertility of population in relation to the number of women aged 15 to 49 instead of the whole population.
General fertility rate (GFR)
Number of live births in one year x 1,000
Number of women aged years

15. General marital fertility rate
In this, the denominator is only the married women in age group
Age specific fertility rate
Number of live births to mothers of a specified age group x 1000
Mid-year female population of same age group

16. Total fertility rate
From age specific fertility rates, a further measure called the total fertility rate (TFR) can be calculated.
It gives an estimate of the average number of children born to a woman throughout her reproductive age as per' prevailing specific fertility rates.

17. Measures of Morbidity
Morbidity, illness, sickness or morbid condition mean deviation from a state of physical or mental well-being as a result of disease, injury or impairment.
In a given population morbidity for a given time may be measured in terms of new cases (incidence) or In terms of new and old cases combined (prevalence).

18. Spell of sickness means the duration of one illness only.
1. Incidence Rates
Incidence tells how often an event occurs in a population over a period of time such as' a week. a month. a year, etc .. e.g .. malaria or typhoid.
i.e .. occurrence of new cases during a specified week, month or calendar year. etc.
Spell of sickness means the duration of one illness only.
In a defined period, one may have two spells. e.g .. two colds in 6 months.
The morbidity rates may be calculated for spells or persons and the same may be mentioned in brackets. The denominator for calculation of rates is the mid-period popu­lation exposed to risk.
Incidence or inception rate (spells)

19. Total number of new spells of illness during a defined period
= x 1,000
Population exposed to risk in the same period

20. . Prevalence Rates
Prevalence indicates how common is an event in a popula­tion. It is of two kinds:
Period prevalence
It is Used to measure the frequency of an illness in existence during a defined period (day, week, month, year, etc). It includes all the cases. in the defined period-old and new cases occurring 'during the same period.
Total number of new and old cases found during a specified period
= X 1,000
Population exposed to risk at the same period

21. b. Point prevalence This term is used to measure the num­ber of cases of illness. new and old. existing at a particular point of time, such as at 2 PM on Monday. the 15th July
Point prevalence
Total number of new and old cases found at a particular point of time
= x Population exposed to risk at the same point of time

22. In a village with a population 5,000, 20 new cases of cholera occurred in January '1975 and 42 cases in 1976 in the months of June, July and August.
Calculate monthly morbidity rate in 1975 and 1976.
Monthly morbidity rate in 1975 = 20/5000x 1000 = 4.
ie .. four cases per thousand per month and
Monthly morbidity rate in 1976
42/3x5000 x 1000 = 2.8/ 1,000/month.

23. There were 45 motor accidents in a town with a population of 69,000 in the year Calculate the incidence rate of accidents.
Incidence rate = 45/69000 x 1000 = 0.65/ 1,000 per year
Traffic police in a town or any large town makes use of this index to assess the benefit of their traffic control measures year by year.

24. Tuberculosis survey was done in a town with 15,000 population
Tuberculosis survey was done in a town with 15,000 population. It was found that 27 cases were radiologically positive while 6 were sputum positive. Calculate the point prevalence rate of sputum positive cases at the time of survey.
Prevalence rate of sputum positive cases
= 6 x 1000 = 0. 4/ 1 000
15,000

25. If 12 cases of diabetes mellitus were found in 15,000 population in a particular year. calculate the prevalence rate.
Prevalence rate= 12 x 1,000 =0.8/1000/year
15,000
Morbidity rates may be calculated per 1, ,000 or 1, depending upon the morbidity load in the com­munity.

26. Incidence rates are usually calculated for acute disease such as cholera. measles. diphtheria. burns. etc .. as their onset is sharply defined.
Prevalence rates are determined for chronic illnesses such as leprosy, tuberculosis, filariasis, cancer, diabetes, hypertension etc. where the onset is very ill-defined. These rates measure the epidemiological situa­tion. suggest priority in measures to be adopted and assess the progress made in the control of a disease.

27. Measures of Mortality
i. Crude Death Rate
It is the most commonly used vital rate as it is easy to compute. It measures the decline in population due to mortality in general, without specifying the factors that influence the deaths such as age-sex composition of population, occupation, causes of death, etc.
Crude death rate
Number of deaths which occurred among the population of a given geographic area during a given year
= x1000
Mid-year total population of the given geographic area during the same year
Crude death rate may also be written as:
CDR = D/P x 1,000 where D stands for total deaths and P for total population.

28. Specific Death Rates
They are calculated to find the mortality experience in different sections of the population such as infants, mothers, males and industrial workers or mortality due to different causes such as tetanus and tuberculosis.
Age-sex death rates are high among the infants and the old and are lowest in the age group years
a. Age specific death rate
Number of deaths in the specified age group
= X 1000 Mid-year population of the same age group

29. Death rates under' one year of age or infant mortality rate
They have special significance as they are very sensitive indices of health services and socio-economic advancement.
Low rates indicate good MCH, obstetric. immunisation and health education services, sanitary environments and ade­quate nutrition.

30. . Still birth rate or late foetal death rate
Foetal deaths after 28 weeks of gestation
= x1000
Live births + still births

31. Perinatal mortality rate
Still births and early neonatal deaths are attributed to similar causes, hence a single rate called perinatal mortality rate is calculated.
It combines:
_ foetal deaths after 28 weeks of gestation when the foetus becomes viable,
- deaths during labour, and
- deaths within seven days of neonatal life.

32. Late foetal deaths (after 28 weeks or more) + deaths under one week
Perinatal mortality rate
Late foetal deaths (after 28 weeks or more) + deaths under one week
= x 1000
Total births (live + still)

33. C. Neonatal mortallty rate
Number of deaths upto 28 days of life
= x 1,000
Number of live births
The causes of mortality in this period are antenatal. natal and postnatal. It may be divided into early neonatal up to one week. late neonatal after one week and up to the end of fourth week.

34. D. Post-neonatal mortality or late infant mortality rate
Deaths after 28 days of life up to one year
= x Live births

35. In a town with a population of 50,000
In a town with a population of 50,000. there were 2000 births and 200 infant deaths in the year 1966.
Of these 80 infants died in the first 28 days of life and 40 of them died in the first week of life. There were 110 still births in the same year.
Calculate infant mortality rate, perinatal, neonatal and post-neonatal mortality rates.
Infant mortality rate 200/ 2000 x 1,000 = 100
PMR / x 1,000 = per thousand

36. Neonatal mortality rate 80/ 2,000 x 1,000 = 40 per thousand
Post-neonatal mortality rate
= x 1,000 = 60 per thousand.

37. Sex specific death rate - female mortality rate is higher than that of males till the age of 35 due to neglect and repeated child-bearing.
Male death rate _ Male deaths x 1000
Mid-year population of males
Age-sex specific death rate It gives the rate for specific age and sex e.g.
Death rate of women in reproductive age group 15-49
= Female deaths in age group 15-49
- Female population of age group 15-49

38. Maternal mortality rate
This rate is important when applied to deaths in mothers owing to puerperal or maternal causes and is specifically known as maternal mortality rate.
Number of deaths due
= to puerperal causes in females x 1,000 Number of live births
Puerperal or maternal deaths include those due to complica­tions of pregnancy. child-birth and puerperium.

39. Cause-specific death rate Cause-specific death rates are computed for the total population.
Numerator is often too small hence the rates may be calculated per instead of per 1,000 to avoid small decimal figures.

40. In country having a population of 430 million
In country having a population of 430 million. 5,00,000 people died of tuberculosis. 50,000 of smallpox. 86,000 of tetanus. 3, of cancer and 6,10,000 of coronary heart disease in Calculate the cause specific mortality rates per 1,00,000
Tuberculosis Death Rate
= x = per
Smallpox DR
50.000
= x = per
Tetanus DR _
x = 20 per
Cancer DR _
x = per
Coronary heart disease DR
6,10000
= x 1.00,000 = per

41. Proportional mortality rate
In this, death rates due to different causes are compared by expressing them in percentages of the crude or total death rate.
Suppose crude death rate is 20 and DR due to tuberculosis is 2. then the tuber­culosis
DR = 2/20 x 100. i.e .. 10% of the total.
An increase in the proportional mortality may be due to an increase in the number of deaths from that cause but it can also be due to a decrease in the total number of deaths from all causes. Similarly. decrease in the proportional mortality could be due to an increase in the total number of deaths.

42. Case Fatality Rate (CFR)
It is the ratio of deaths due to a particular disease to the number of persons who suffered from the same disease.
Number of deaths due a particular disease
CFR = x 100
Number of cases of the same disease

43. In a cholera epidemic caused by Asiatic cholera
In a cholera epidemic caused by Asiatic cholera. Vibrio cholerae, 64 cases died out of 160 attacks while in typhoid before chloramphenicol. 60 died out of 200. Find the case fatality rates of both and compare .
64 x 100
Cholera case fataIity rate = = 40%
Typhoid case fatality rate = 60x100 = 30%
200
Thus, cholera had a fatality higher than typhoid. This rate is also useful to compare the effect of treatment or any other procedure adopted to reduce the mortality such as chloram­phenicol treatment in typhoid and preventive inoculation in cholera.

44. Application of Rates and Ratios of Vital Indices
Analysis of health statistics by computing various indices in the form of rates and ratios leads one to draw some con­clusions. Interpretation of conclusions should be done care­fully to make suitable recommendations to deal with the community health problems.
Biased conclusions due to defect in registration. collection and compilation of data are very likely, When the records are not reliable, it is better to carry out sample surveys, following the rules for selection and inquiry strictly.

45. Monitoring of illness in the Community
Morbidity rates From the incidence or prevalence of dis­eases, not only is the extent of illnesses in the country found but also conclusions are drawn about the role of environmental conditions.
High incidence of cholera and gastroin­testinal infections means poor water supply, drainage and disposal of refuse.
High prevalence of tuberculosis means poor socio-economic conditions. Certain living conditions contribute to individual and community health.

46. These can be assessed, such as food and nutrition. housing
These can be assessed, such as food and nutrition. housing. place of work. recreation. social security. atmospheric pollution. etc. These are indicative of "level of living" and measure whether the desired standards of living have been achieved or not. They do not measure the actual health condition.
Thus negative indices of community health are depended upon to draw conclusions about the health of a community. Of these indices, one should search for the index that can be the most comprehensive yardstick and then find the, specific ones.

47. Comprehensive Indicators that Measure Health
1. Proportional mortality indicator
As defined before, it is obtained as a percentage of the deaths at 50 years and above to the total deaths. There are more old people in developed countries and large number of deaths are there at the age of 50 years and over.
In countries with poor health conditions and poor health services mortality is higher in younger children, in mothers due to specific causes and in other due to preventable and controllable communicable diseases.
So, higher the percentage value of this index. the better is the health condition of the community.

48. 2. Expectation of life
Longevity of life worked out by the life table method, it is also a comprehensive measure of com­munity health and summarises the mortality experience at all ages of life.

49. In all developed countries,women live longer on an average by 5 years or more.
In USA expectation of life at birth was in males and in females,the same ratio in Thailand was and
Number of old people above 60 years was 5.1 % and in 1981 it was 5.6%.
3. Number of females
It is always higher than males in socio-economically advanced countries while in the under­developed countries, number of males is higher than females due to better health care of males.
4. Crude death rate This is usually the index available but should be made use of. only after adjusted or standardised rates are worked out. It is useful for short-term comparisons.

50. Morbidity data collected in specific surveys can be a good indicator of comprehensive or specific health services.
Nutritional status, absenteeism due to sickness in schools and industries and development of children from 1-4 years may be useful guides in the assessment of community health.