Lecture 4 Flashcards
What is human demography (HD)?
HD studies changes in population size, structure and geographic distribution
(HD) Changes in population size, structure and geographic distribution are the result of?
fertility, mortality, and migration
why should health researchers care about demography and factors that affect population dynamics?
- demography
- economic, social, cultural factors as well as ecological and biological processes
- population health
All affect one another
HD is nourished by many different disciplines that analyse different aspects of the relationships between economic, social, cultural and biological processes that affect population dynamics such as: economic, sociology, history, biology, anthropology, etc.
what does an expanding population pyramid look like?
super wide at the bottom (young years) and gets super thin at the top (older years)
Stationary pyramid
relatively equal medium width throughout all years until late years very thin
- zero growth
constrictive pyramid
thinner at the bottom/younger years, wider in upper middle and relatively equal till latest years
- negative growth
how is population growth measured?
r = birth rate + [net migration] - death rate
net migration = immigration - emigration
crude mortality rates
m = (d/r) 1000
d = number of deaths during a year
r = number of individuals “at risk of dying”
age specific mortality rates
mx = (dx/Nx) 1000
d = number of deaths to individuals in the 4th age category during a year
N = number of individuals in the 4th age category
x = can be infants or other variables
mortality - two important parameters
- life expectancy
- average number of years remaining for an individual (e.g., life expectancy at birth) - age patterns of mortality
- age-specific mortality rates (fraction of cohort alive at the START OF THE INTERVAL)
- age specific mortality curves
what are some variability in mortality
sex differentials: women tend to live longer than males (with som exceptions) in contemporary industrialised populations
- geographic variation within populations
- variation between nations
life expectancy by country
World population as a whole = 73.4 years (76 females/70.8 males)
Longest life expectancy at birth - Hong Kong: total pop: 85.83 years, males:83, females:88.66
Shortest life expectancy at birth - Chad: 53.68 years, males:52.01, females:55.41
Developed countries: mortality started decreasing around 1920
biological regulation of human fertility
- variation in male and female fecundity
variation in female fecundity is critical for HD due to what factors?
- age
- energetics (pregnancy, childbirth, and lactation, require significant energy)
- lactation (Prolonged lactation can lead to longer inter-birth intervals which reduce the overall reproductive rate. Successful lactate can be influenced by health, nutrition, and SES, which affects child survival rates and maternal health)
- disease
- social environment
variation in female fecundity with age explained by changes in:
- ovarian hormone levels
- frequency of ovulation
- size of the follicle before ovulation
- thickness of the uterine lining
- fetal loss
how can these variations of female fecundity affect population growth?
by affecting reproductive rates (either by slowing them down and or speeding them up)
However, faster reproductive rates (shorter IBI) do not always result in population growth as they can be associated with shorter life spans via increased maternal and child morbidity and mortality
biological regulation of human fertility - variation in female fecundity - diseases
disease
- STDs: blockage of the fallopian tubes
- infections during childbirth: damage to the reproductive tract
- malaria: increase rate of embryonic loss
social regulation of human fertility
Regulation of the formation of reproductive unions:
- variability in age at which unions are formed
- percentage of women who never marry
Exposure to intercourse
- who has sex with whom and when
Probability of conception and birth, given intercourse
- pattern of intercourse
- behavioural regulation of probability of conception and live birth
Patterns of intercourse within reproductive unions:
- spousal separations in migrant labor populations
- honeymoon effect: frequency of intercourse is highest early into marriage
- cultural festivities (e.g., August vacation)
- sexual taboos (e.g., postpartum taboo)
Behavioural regulation of probability of conception and live brith:
- contraceptive use (to limit family size, to space births)
- legislation and attitudes towards elective abortion
the epidemiology transition: changes in mortality patterns
Population growth seen as a result of improvements in sanitary conditions, medical innovations and improvements in nutrition and quality of life in general
demographic transition
- transition from high death and birth rates to low death and birth rates
Associated factors:
- energetic resources
- contraceptive methods
Negative social attitudes towards larger families and increased cost per offspring
changes in mortality patterns - traditional view for the demographic transition
Sanitation and medical innovation resulted in a shift from a greater proportion of infectious diseases (measles, tuberculosis) and resource scarcity to a greater proportion of degenerative disease (cancer, CVD) and problems associate with over abundance of resource and sedentarism (obesity, non insulin dependent diabetes)
changes in mortality patterns in West Europe - McKeown’s Study Findings
McKeown’s study of the historical decline in mortality in England and Wales between 1860-1971 examined four potential causes
- host-parasite interactions
- introduction of effective sanitary systems
- development of modern medicine
- improvements in nutrition
Proximate and ultimate causes of the variation in mortality
Introduction of effective sanitary systems
- specific studies suggest that about 20% of the overall decline in mortality is attributable to improvements in sanitation
Modern medicine
- the decline in mortality due to the development of effective treatments (e.g., decline in tuberculous preceded development of streptomycin by at least 100 years)
Changes in mortality patterns - improvement in nutrition - McKeown
- McKeown concluded that if all other factors are eliminated, the one remaining, nutrition, must be corrected
- Little empirical evidence supporting the hypothesis that nutrition alone could explain these transitions
Perhaps the demographic transition can result from multiple factors acting in synergy
