# ELEMENTS OF DEMOGRAPHY

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ELEMENTS OF DEMOGRAPHY
Isaac A. Ilano, MSPH, Ed.D Associate Professor Department of Family and Community Medicine

DEMOGRAPHY is the mathematical and statistical study of the size (# of persons in a population), composition (measurable characteristics) and spatial distribution (arrangement of the population in space in a given time) of human populations, and of changes over time in these aspects, through the operation of the five processes of: - Fertility - no. of children being born Mortality - deaths Marriage - age of getting married Migration - in and out migration Social mobility

USES OF DEMOGRAPHIC DATA

To determine the number and distribution of a population in a certain area for planning, priority setting, and for purposes of fund allocation. To determine the growth (or decline) and dispersal of population in the past.

To establish a “causal relationship” between population trends and various aspects of social organization. To predict future developments and their possible consequences.

SOURCES OF DEMOGRAPHIC DATA
Census - may be defined as the total process of collecting, compiling and establishing demographic, economic and social data pertaining, at a specified time or times, to all persons in a country or delimited territory.

Essential Features of a Population Census:
Individual enumeration - each individual is enumerated separately and the characteristics of each person are recorded separately. Universality within a defined territory - all people are included

Simultaneity – a population is enumerated
Simultaneity – a population is enumerated using one reference date with respect to a well defined point in time Periodicity - censuses are taken at regular intervals. Previously, every 5 years. Currently, every 10 years.

Types of Census Allocation:
De jure method - individuals are assigned to the place of their usual residence, without reference to where they were actually enumerated during the census.

De facto method - individuals are allocated to the areas in which they are physically present at the census date, without reference to where they usually live.

Usual Information Obtained in a Census:
Geographic information - location at time of census Household or family information - household/ family size Personal characteristics - sex, age, marital status Economic characteristics - occupation Cultural characteristics - language/s spoken Educational characteristics - literacy, educational attainment Fertility data - number of children ever born

SOURCES OF DEMOGRAPHIC DATA….cont’n.
2. Sample Surveys - studies done on a subset of a population. 3. Registration System - deals with continuous recording of vital events. Compulsory of births, deaths and marriages 4. Continuing Population Registers - continuous recording of information about the population.

SOURCES OF DEMOGRAPHIC DATA….cont’n.
Other Record Systems Voter’s Registration School Enrollment Income Tax Returns Social Security Systems

IMPORTANCE OF STUDYING THE AGE AND SEX COMPOSITION OF A POPULATION
Almost any measurements that can be taken of human beings will show substantial variation by age and sex Ex. Illness and death characteristics are affected by age and sex.

The age and sex structure of a population is the basic demographic determinant of a nation’s manpower supply. It influences requirements for various essential goods and services. A population’s age and sex structure is both a cause and an effect. It determines the rate of population growth.

1. THE SEX COMPOSITION OF A POPULATION
Tools for describing the sex composition No. of males a Sex Ratio = x 100 No. of females > The resulting figure represents the number of males for every 100 females in the population. a Sex Structure = sex ratio for each group (life cycle) Ex. sex ratio for pre-schoolers, sex ratio for school children, etc.

Some generalizations of the Sex Composition of a Population:
b.1 Sex ratio at birth is generally There are more males than females in the younger age group. b.2 The sex ratio tends to decrease with age, eventually falling below This is because age- specific mortality rates are usually higher among males than females.

b. 3. Sex ratio is higher in rural areas than in. urban areas
b.3 Sex ratio is higher in rural areas than in urban areas. There are less females and more males in the rural areas. b.4 Frontier communities and colonies have higher sex ratios

2. THE AGE COMPOSITION OF A POPULATION
Tools for Describing the Age Composition a.1 Median Age of the Population - divides the population into 2 equal parts. It is the age below which 50% of the population fall and above which the rest of the other 50% of the population fall.

Pop’n aged 0-14 + Pop’n aged 65+
a.2 Dependency Ratio - represents the number of dependents that need to be supported by every 100 population in the working age group. Pop’n aged Pop’n aged 65+ Dependency Ratio = x100 Pop’n. aged 15-64 The dependency ratio provides an index of the age-induced economic drain on manpower resources.

b. Factors Affecting the Age Composition
b.1 Fertility- a higher fertility leads to a younger population b.2 Urban- rural differences In general, an urban population tends to have an older age composition than a rural population as a result of the fertility factor.

b. 3 Peace and Order Situation (War)
b.3 Peace and Order Situation (War) Immediate post-war periods bring about a baby boom and a resultant younger population b.4 Cultural practices, example, age at marriage. Women in rural areas get married early (at 20 years old women are already considered old maid).

POPULATION PYRAMID - graphical representation of the age and sex composition of a population.

Steps in Constructing a
Population Pyramid 1. Data Needed > Population distribution by age and sex 2. Compute the percentage falling under each age - sex group, using the total population as the denominator.

Construct the population pyramid using the percentages computed
Construct the population pyramid using the percentages computed. The following general rules are followed: a. Each group is represented by a horizontal bar, with the first bar at the base of the pyramid representing the youngest age group

The bars for males are traditionally presented on the left side of the central vertical axis while the bars for females are presented on the right side. c. The length of each bar corresponds to the % of the population falling in the specific age and sex group being plotted.

Number and Percent Distribution of the Population
by Age and Sex, Batangas, 1990 MALE FEMALE Age group (yrs) No. % 0 – 4 5 – 9 10 – 14 15 – 19 20 – 24 25 – 29 30 – 34 35 – 39 40 – 44 45 – 49 50 – 54 55 – 59 60 – 64 65 – 69 70 – 74 75 – 79 80 + 96,980 99,768 94,039 82,979 72,587 58,661 50,732 43,307 34,962 26,664 22,360 17,613 13,612 10,084 7,849 5,929 4,582 6.6 6.8 6.4 5.6 4.9 4.0 3.4 2.9 2.4 1.8 1.5 1.2 0.9 0.7 0.5 0.4 0.3 91,271 93,893 88,962 78,926 69,241 56,411 49,523 42,852 35,773 28,296 24,373 19,895 15,820 13,226 9,959 7,489 6,605 6.2 6.0 5.4 4.7 3.8 1.9 1.7 1.3 1.1 ALL AGES 742,708 50.3 732,515 49.7 TOTAL POPULATION = 742, ,515 = 1,475,223

Population Distribution by Age and Sex Batangas, 1990
Males Age Females 80 + 45 -49 5 - 9 0 - 4 8 6 4 2 0 Percent 0 *Assuming that the oldest person is 100 years old.

Since population pyramids represent the age and sex distribution of a population, this representation may take on various shapes, some of which do not resemble a pyramid at all. Several types of population pyramids and their unique features are represented by the following figures

Type 1 pyramid has a broad base and gently sloping sides
Type 1 pyramid has a broad base and gently sloping sides. This pyramid is typical of countries with high rates of birth and death. The population can also be characterized as having a low median age and high dependency ratio.

Type 2, compared to Type 1, has a broader base and its sides bow in much more sharply as they slant from the 0-4 age group to the top. This second type of pyramid is typical of countries that are beginning to grow rapidly because of marked reduction in infant and child mortality, but are not yet reducing their fertility. As a consequence of a rapidly increasing population, the median age is decreasing.

The third type of pyramid does not resemble a pyramid at all, but an old-fashioned beehive. This age-sex structure is typical of countries with levels of birth and death rates found in the Western European countries. Because of the low birth rates, the median age is highest and its dependency ratio is lowest compared with other age-sex structures. The dependents are mostly elderlies.

The fourth type of pyramid, a bell-shaped one, is a transitional type of pyramid. This represents a population which, after more than 100 years of declining birth and death rates, has reversed the trend in fertility while maintaining the death rate at low levels.

The last type of population pyramid represents a population which is experiencing a marked and rapid decline in fertility. If this decline continues, however, the absolute loss in numbers will soon become apparent. The population represented by this pyramid has usually a low death rate and as mentioned above, has reduced its birth rate very rapidly

CONSEQUENCES/ EFFECTS OF AGE AND SEX STRUCTURE
1. Consumption Patterns - If the population has a large proportion of children, there is a need for greater spending on food and education. On the other hand, a large proportion of old persons necessitate greater spending for medical care and social services.

CONSEQUENCES/ EFFECTS OF AGE AND SEX STRUCTURE…cont’n.
2. Death rate is affected by age structure. A younger population has a lower Crude Death Rate. 3. Migration rates. Young adults tend to be more mobile than middle aged and elderly persons 4. Variations in age and sex structure affect the probabilities of marriage for men and women 5. Power structure. An older population is usually more conservative.

OTHER IMPORTANT POPULATION CHARACTERISTICS
1. Marital status - affects fertility and mortality rates. The greater the population of married women, the higher the Crude Birth Rate. 2. Religious composition 3. Lingual composition 4. Economic composition 5. Educational composition

POPULATION ESTIMATION
Tools in Describing Change in Population Size a. Natural Increase = number of births -number of deaths b. Rate of Natural Increase = CBR - CDR

c. Relative Increase in Population Size (RI)
= Measures the % increase or decrease in population count relative to an earlier count Pt – Po RI = x 100 Po Where: Pt = population at present time, t Po = population at earlier time, o

d. Absolute increase in population per year (b)
Pt – Po b = x 100 t Where: t = no. of years between time o and time t

Annual rate of growth (r) = formula for r
Annual rate of growth (r) = formula for r depends on the assumption taken regarding the nature of the rate of growth of the population per year. This rate of growth takes on the assumption that the population is changing at a constant rate per year.

Types of Estimates and Projections
1. According to detail desired 2. According to time reference 3. According to Method of Estimation

1. According to Detail Desired
a. Total population vs. population subgroups b. Population by selected characteristics (age and sex) Examples: Estimate nos. of infants Estimate nos. of mothers

2. According to Time Reference
a. Intercensal Estimates - refers to a date intermediate to two censuses and take the results of these censuses into account.

b. Postcensal Estimates - refers to a past or
b. Postcensal Estimates - refers to a past or current date following a census and takes that census and possibly earlier censuses into account, but not later censuses. c. Projections - refers to dates following the last census for which no current reports are available. The distinction between these two types are not quite clear-cut.

3. According to Method of Estimation
a. Component Method (Inflow – Outflow Method) consists of adding natural increase and net migration for the period since the last census to the latest count or the latest previous estimate best implemented where continuous population registers are maintained Pt = Po + (B-D) + (I-O)

b. Mathematical Methods
1. Arithmetic Method assumes an equal amount of increase every year 2. Geometric Method assumes that the population increases or decreases at a constant rate, over each unit of time

3. Exponential Method assumes a constant rate of increase or decrease, with the population size changing continuously at every infinitesimal amount of time assumes population growing by the seconds.

RATIO - is a relative number expressing the magnitude of one occurrence or condition in relation to another. Ex. 1. Sex Ratio = Number of Males x 100 Number of Females 2. Dependency Ratio = No. of persons aged yrs & over x 100 No. of persons aged 15-64

RATE - refers to the occurrence of events over a given interval of time relative to the size of the population at risk of the event during the same time interval. Ex. Crude Birth Rate (CBR) = No. of live births in a yr. x F Average Population

It is necessary that the numerator of the rate should be defined according to:
the character of the event in question; the geographical area to which the event belongs; the time period within which it occurred.

Events should be tabulated by:
date of occurrence than by date of registration by place of residence rather than by place of occurrence

Important factors to consider in interpreting rate and ratio:
1. The source of the numbers that entered into the numerator and denominator, how were they obtained? 2. Do they represent an accurate count of the event under study? 3. What is the time period involved? A week? Month? Year?

4. Does the rate obtained after analysis measure what it is supposed to measure?
5. Is the magnitude of the rate reasonable in relation to what one may expect the rate to be?

Mortality Rates - measures the probability of dying
Different kinds of Mortality rates: Crude Death Rate (CDR) = Total deaths, all causes x F Average Population - measure the decrease of the population due to death, the force of mortality or the probability of dying

Disadvantage: not a very useful method of comparing population groups that are radically different in composition and may give misleading conclusions.

2. Cause-of-death rate (CSDR)
= No. of deaths from a particular cause x F Average Population most causes of death rates are computed on total population, except IMR and some age-specific rates.

3. Specific Death Rate: Age-specific-death rate
- necessary to study in detail the mortality conditions in a community Age-specific-death rate = Deaths, all causes in particular age grp x F Average population of same age group

b) Age-and-sex specific death rate
= Deaths in partic. age & sex group x F Average pop’n of same age & sex grp. c) Age-sex & cause-specific death rate = Deaths from partic. cause in sex & age group x F Ave. pop’n of same age & sex grp

4. Proportionate Mortality rate
- this rate may be cause, age, sex, occupation etc. - used for describing the relative importance of different fatal diseases in the population, of different ages, sex, occupation, etc. - can be calculated for specific age group useful for determining the order of importance of cause of death in different age groups. denominator: total death all causes

Swaroop’s Index: the higher this rate the better is the health status of the population - this is a good indicator in comparing the health status of different countries, since it is very simple and most of the information needed are available. total deaths 50 yrs old & above total death, all causes SI - X 100

5. Infant Mortality Rate (IMR)
= No. of deaths below 1 yr x F No. of livebirths one of the most sensitive indices of the health condition of the general population

6. Neonatal-Mortality Rate (NMR)
= No. of deaths below 28 days x F Total livebirths - deaths in this period are mostly due to prenatal causes and are more difficult to reduce than the post-neonatal death rate

7. Post-Neonatal Mortality Rate (PNMR)
= Infant deaths 28 days to<1yr x F Total livebirths 8. Fetal Death Ratio (Stillbirth rate) = Fetal deaths 28 wks. & over gestation x F Total livebirths

9. Perinatal Mortality Rate
= Fetal deaths, 28 wks & over gestation + infant deaths < 7 days x F Total livebirths 10. Maternal Mortality Rate = Deaths among women directly due to pregnancy, labor & puerperium x F Total livebirths

measure the risk of dying from causes associated with childbirth
ideal denominator in the number of women but since this number is unknown, the number of livebirths has been adopted for practical reasons. caution must be exercised in comparing this rate from different places.

11. Case Fatality Rate = No. of deaths from a particular disease x F
No. of cases of same disease modified by the completeness of both reported cases and deaths.

Morbidity Rates - refers to diseases or sickness

1. Incidence Rate Two general types of Morbidity Rates:
= No. of New Cases of Dse. over a prd. of time x F Population at risk this is a broad term & the figures in the numerator is usually obtained from notification during an interval of time, usually a year and hence are usually underenumerated

2. Prevalence Ratio = No. of existing old & new cases at a point in time x F Total Population this is a static count of the number of individuals suffering from a particular disease in a particular instant of time

Fertility Rates 1. Crude Birth Rate (CBR)
Most commonly used of fertility rates are: 1. Crude Birth Rate (CBR) = No. of livebirths in a year x F Average Population this rate gives the number of livebirths relative to the total population data is always available  widely used

2. General Fertility Rate (GFR)
= No. of livebirths in 1 year x F No. of Women yrs more appropriate measure of fertility

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