Presentation on theme: "ELEMENTS OF DEMOGRAPHY"— Presentation transcript:
1ELEMENTS OF DEMOGRAPHY Isaac A. Ilano, MSPH, Ed.D Associate Professor Department of Family and Community Medicine
2DEMOGRAPHY 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 bornMortality - deathsMarriage - age of getting marriedMigration - in and out migrationSocial mobility
4To 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.
5To establish a “causal relationship” between population trends and various aspects of social organization.To predict future developments and their possible consequences.
6SOURCES 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.
7Essential 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
8Simultaneity – a population is enumerated Simultaneity – a population is enumerated using one reference date with respect to a well defined point in timePeriodicity - censuses are taken at regular intervals. Previously, every 5 years. Currently, every 10 years.
9Types 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.
10De 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.
11Usual Information Obtained in a Census: Geographic information - location at time of censusHousehold or family information - household/ family sizePersonal characteristics - sex, age, marital statusEconomic characteristics - occupationCultural characteristics - language/s spokenEducational characteristics - literacy, educational attainmentFertility data - number of children ever born
12SOURCES 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 marriages4. Continuing Population Registers - continuous recording of information about the population.
13SOURCES OF DEMOGRAPHIC DATA….cont’n. Other Record SystemsVoter’s RegistrationSchool EnrollmentIncome Tax ReturnsSocial Security Systems
14IMPORTANCE 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 sexEx. Illness and death characteristics are affected by age and sex.
15The 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.
161. THE SEX COMPOSITION OF A POPULATION Tools for describing the sex compositionNo. of malesa Sex Ratio = x 100No. 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.
17Some 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.
18b. 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
192. THE AGE COMPOSITION OF A POPULATION Tools for Describing the Age Compositiona.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.
20Pop’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 = x100Pop’n. aged 15-64The dependency ratio provides an index of the age-induced economic drain on manpower resources.
21b. Factors Affecting the Age Composition b.1 Fertility- a higher fertility leads to a younger populationb.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.
22b. 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 populationb.4 Cultural practices, example, age at marriage. Women in rural areas get married early (at 20 years old women are already considered old maid).
23POPULATION PYRAMID - graphical representation of the age and sex composition of a population.
24Steps in Constructing a Population Pyramid1. Data Needed> Population distribution by age and sex2. Compute the percentage falling under each age - sex group, using the total population as the denominator.
25Construct 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
26The 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.
27Number and Percent Distribution of the Population by Age and Sex, Batangas, 1990MALEFEMALEAge group (yrs)No.%0 – 45 – 910 – 1415 – 1920 – 2425 – 2930 – 3435 – 3940 – 4445 – 4950 – 5455 – 5960 – 6465 – 6970 – 7475 – 7980 +96,98099,76894,03982,97972,58758,66150,73243,30734,96226,66422,36017,61313,61210,0847,8495,9294,58184.108.40.206.64.94.03.42.220.127.116.11.18.104.22.168.40.391,27193,89388,96278,92669,24156,41149,52342,85235,77328,29624,37319,89515,82013,2269,9597,4896,6056.26.05.44.22.214.171.124.31.1ALL AGES742,70850.3732,51549.7TOTAL POPULATION = 742, ,515= 1,475,223
28Population Distribution by Age and Sex Batangas, 1990 MalesAgeFemales80 +45 -495 - 90 - 486420 Percent 0*Assuming that the oldest person is 100 years old.
29Since 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
30Type 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.
31Type 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.
32The 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.
33The 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.
34The 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
35CONSEQUENCES/ 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.
36CONSEQUENCES/ 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 persons4. Variations in age and sex structure affect the probabilities of marriage for men and women5. Power structure. An older population is usually more conservative.
37OTHER 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 composition3. Lingual composition4. Economic composition5. Educational composition
38POPULATION ESTIMATION Tools in Describing Change in Population Sizea. Natural Increase= number of births -number of deathsb. Rate of Natural Increase= CBR - CDR
39c. Relative Increase in Population Size (RI) = Measures the % increase or decrease in population count relative to an earlier countPt – PoRI = x 100PoWhere: Pt = population at present time, tPo = population at earlier time, o
40d. Absolute increase in population per year (b) Pt – Pob = x 100tWhere:t = no. of years between time o and time t
41Annual 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.
42Types of Estimates and Projections 1. According to detail desired 2. According to time reference 3. According to Method of Estimation
431. According to Detail Desired a. Total population vs. population subgroupsb. Population by selected characteristics (age and sex)Examples: Estimate nos. of infantsEstimate nos. of mothers
442. According to Time Reference a. Intercensal Estimates - refers to a date intermediate to two censuses and take the results of these censuses into account.
45b. 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.
463. 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 estimatebest implemented where continuous population registers are maintainedPt = Po + (B-D) + (I-O)
47b. Mathematical Methods 1. Arithmetic Methodassumes an equal amount of increase every year2. Geometric Methodassumes that the population increases or decreases at a constant rate, over each unit of time
483. Exponential Methodassumes a constant rate of increase or decrease, with the population size changing continuously at every infinitesimal amount of timeassumes population growing by the seconds.
49RATIO- is a relative number expressing the magnitude of one occurrence or condition in relation to another.Ex.1. Sex Ratio= Number of Males x 100Number of Females2. Dependency Ratio= No. of persons aged yrs & over x 100No. of persons aged 15-64
50RATE- 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 FAverage Population
51It 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.
52Events should be tabulated by: date of occurrence than by date of registrationby place of residence rather than by place of occurrence
53Important 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?
544. 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?
55Mortality 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
56Disadvantage:not a very useful method of comparing population groups that are radically different in composition and may give misleading conclusions.
572. Cause-of-death rate (CSDR) = No. of deaths from a particular cause x FAverage Populationmost causes of death rates are computed on total population, except IMR and some age-specific rates.
583. Specific Death Rate: Age-specific-death rate - necessary to study in detail the mortality conditions in a communityAge-specific-death rate= Deaths, all causes in particular age grp x F Average population of same age group
59b) Age-and-sex specific death rate = Deaths in partic. age & sex group x FAverage 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
604. 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 groupuseful for determining the order of importance of cause of death in different age groups.denominator: total death all causes
61Swaroop’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 & abovetotal death, all causesSI -X 100
625. Infant Mortality Rate (IMR) = No. of deaths below 1 yr x FNo. of livebirthsone of the most sensitive indices of the health condition of the general population
636. Neonatal-Mortality Rate (NMR) = No. of deaths below 28 days x FTotal livebirths- deaths in this period are mostly due to prenatal causes and are more difficult to reduce than the post-neonatal death rate
647. Post-Neonatal Mortality Rate (PNMR) = Infant deaths 28 days to<1yr x FTotal livebirths8. Fetal Death Ratio (Stillbirth rate)= Fetal deaths 28 wks. & over gestation x FTotal livebirths
659. Perinatal Mortality Rate = Fetal deaths, 28 wks & over gestation + infant deaths < 7 days x FTotal livebirths10. Maternal Mortality Rate= Deaths among women directly due topregnancy, labor & puerperium x FTotal livebirths
66measure 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.
6711. Case Fatality Rate = No. of deaths from a particular disease x F No. of cases of same diseasemodified by the completeness of both reported cases and deaths.
691. Incidence Rate Two general types of Morbidity Rates: = No. of New Cases of Dse. over a prd. of time x FPopulation at riskthis 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
702. Prevalence Ratio= No. of existing old & new cases at a point in time x FTotal Populationthis is a static count of the number of individuals suffering from a particular disease in a particular instant of time
71Fertility 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 FAverage Populationthis rate gives the number of livebirths relative to the total populationdata is always available widely used
722. General Fertility Rate (GFR) = No. of livebirths in 1 year x FNo. of Women yrsmore appropriate measure of fertility