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Chapter 4

SOC312H1 Chapter 4 Demographic Composition.docx

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Brent Berry

Chapter 4: Demographic Transition Age Structure: - Process of birth, death, and migration –the three key demographic processes –are all age dependent - Age is also determining factor in the incidence of other demographic events, including cohabitation, marriage, divorce, remarriage, widowhood, labour force activity, and unemployment - All demographic phenomena is that they are conditioned by sex o For example, females enjoy lower death rates than males in most circumstances; the chances of long distance relocation are usually greater for males than for females Principles of Age and Sec Composition Population Age Distribution - Demographers typically interested in three segments of the population: those under 15 (youth), those aged 15-64 (working age), and those aged 65 and older (post-retirement) - Usefulness of three broad age categories? o Get a sense of “economic dependency’ burden in a given society. By taking ratio of youth + old age dependents to the working age population = a measure of society’s overall dependency on the workers, who must provide for those not in the labour force. 3 associated measures of dependency: total, youth, and old age o Total dependency ratio (TDR) = P 0-14+ P65+/ P15-64 100 o Can be broken down into component parts: youth dependency ratio (YDR) = P 0- 14 /15-64 o Old age dependency ratio (ODR) = P 65+/ P15-64 100 - A dependency ratio greater than 100 would indicate the presence of more dependents than workers in the population: the higher the ratio, the greater the dependency ‘burden’ on the working population - Ratio below 100 would signify opposition situation - Values of dependency ratios are closely related to a population’s age distribution Age Pyramids - % males in age group x = # of males in age group x / total population x 100 - % females in age group x = # of females in age group x / total population x 100 Typology of Age Pyramids - Canada’s age structure is very similar to that of most other highly industrialized countries today - The shape of the distribution deviates somewhat from that of a true pyramid in the geometric sense. - The base is narrow, there is a noticeable budge in the ages between 35 and 55, and the top of the pyramid –representing those over the age of 65 –is fairly wide - Age distributions change as a society’s birth and death rates shift in the process of demographic transition has proposed 3 prototypical types of age pyramids and mortality conditions, and therefore population growth rate - Rapidly growing population pyramids (Type A) are characterized by a wide base and a narrow top - In recent decades some developing countries have been gradually moving away from the Type A (rapidly growing population)(pg. 99) form and taking a more triangular shape as the part of the distribution corresponding to the reproduction ages, roughly 15 to 50, grows wide. This type of age compositions are growing rapidly - In Type B (constant growth population) populations the age structure remains constant indefinitely; represents a stationary population with constant age-specific birth and death rates, and therefore a constant rate of growth; no population fits this description exactly but approximates it o Examples like western Europe, as well as Canada, Japan, South Korea, Singapore - Type C (declining population) age distribution is top heavy and base is narrow. These countries are expected to lose population every year as a result of more or less stable negative growth rates (fewer births than deaths) Determinants of Age Composition - Shifts in age composition are produced mainly by changes in fertility and (to a less degree) mortality - Comprehensive account of demographic dynamics that determine whether a population is aging or growing younger was developed by Coale who found fertility to be the major determinant of changes in age composition Stable and Stationary Populations - Stable age distribution: age distribution of the population and its rate of growth would be constant o Stable population can be either increasing or decreasing in size, as long as the rate of change remains constant; what is ‘stable’ is the shape of the age distribution o Stationary population  rate of growth is 0: neither the size of the population nor its age structure changes from year to year; only case in which total number of people in the population and the number and percentage of the population within each of the age categories all remain constant The Relative Importance of Fertility and Mortality - Indicator of mortality is life expectancy at birth –a measure of survival determined by a population’s age-specific mortality rates; the higher the life expectancy, the better the survival conditions in a society - The index of fertility is the gross reproduction rate (GRR), which measures the average number of daughters born to a woman, given a prevailing schedule of age-specific fertility rates; the greater the GGR, the higher the fertility - Level of mortality (expectation of life at birth, e ) 0 - Fertility (the gross reproduction rate, GRR) - Fertility is the key determinant of changing the age composition; morality plays much smaller role - Prolonged life by reducing death rates makes the population somewhat younger, even though a reduction in the death rate increases the average age of death and therefore the number of old people in the population - Sustained mortality reductions in the younger age groups help to increase the numbers of persons in the reproductive-age cohorts, which will eventually go on to bear children when they reach parental age. This has the effect of making the population’s age structure younger - In populations that have passed through demographic transition and are now in the post transition stage, mortality rates in infancy, childhood, and the reproductive ages are already very low and it is the over 60 age segment that experiences major improvements in survival probabilities - Been shown using stable population models that, in general, when mortality declines are concentrated in infancy and early childhood, the effect will be to make the population younger; - If survival improvements are concentrated in the ages above 45, the effect will be to age the population Crude and Intrinsic Growth Rates - Rate of natural increase (RNI) is reported as differences between the crude birth and death rates for a given population o Since the crude birth and death rates don’t take into account age composition, the resulting rate of natural increase is a crude measure of the rate of growth o The intrinsic rate of growth based on a population’s equivalent stable population (ie. The difference between the intrinsic birth and death rates) represents the rate of growth of the population without the confounding effects of age composition Effects of Migration on Age-Sex Structure - in case of our-migration, the impact on the sending society may be noticeable if the numbers leaving are large and concentrated in a specific age category –typically the prime labour force years –and gender the longer the out migration continues, the greater the impact on the age and sex structure of the sending population will be - immigration’s effects on host population’s age structure will largely depend on the size of the age categories into which immigrants are moving, the numbers of immigrants entering those age categories, the gender composition of the immigrants and the intensity of immigration over time - in Canada, age pyramid of immigrant population is shaped more like diamond because most immigrants are concentrated in prime labour ages of 20 to 64 - in some cases, age structure of receiving population may be visible on only one side of age pyramid either male or females. This imbalance would tend to affect age distribution in these countries in 2 ways o 1 : would shift overall sex ratio of the population in favour of either males or females, depending on which sex is most affected by either in or out migration nd o 2 : sex ratios in affected age groups would be distorted, with an oversupply of either females or males Age Distribution as Demographic Memory - A fundamental principle of stable population theory is that two populations with radically different age structures will converge to identical age compositions if the two populations have identical age-specific birth and death rates over 70 years or more - Age distributions gradually ‘forget’ their past  ergodic property of populations - Takes roughly a century for a population’s age structure to change completely Population Momentum - M = size of stationary population / size of the initial population o Value greater than 1 = population would grow as a result of momentum generated by youthful age structure of the population. o Value of 1 = no momentum (stationary population) o Value below 1 = population decline (negative momentum) - Shortcut formula for driving the growth factor that represents population momentum has been worked out by Keyfitz o M = be / 1, 000 √ NRR o o Where M is momentum, b is the population’s crude rate birth date, EOis its life expectancy at birth and NRR is the net reproduction arte of the population before t drop in fertility to the replacement level. Thus, if a population has a crude birth rate of 35, a life expectancy of birth at 5, and a net reproduction rate of 2.5, it would grow by a factor of 1.439 before it leveled off:  M = 35 x 65 / 1000 √ 2.5 = 1.439 - The analysis of population momentum is a useful for planning purposes. If a society with a rapidly growing population wishes to reduce its rate of growth, it must be prepared to look far into the future. o a growing population that abruptly reduces its fertility to replacement level and maintains it there will still grow for two generations or so. This residual growth will be even large if the decline to replacement fertility takes place gradually - NRR is a measure of population reproductively – the extent to which mothers replace themselves by bearing daughters. NRR is approximately one half of the value of the total fertility rate (TFR). Thus a TFR of 2.1 means that women on average are bearing one
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