Appearances and realities

Demographic point of view

Demographic toolkit

Rules of the game

• Examples that involve commonly observed regularities accompanied by (sometimes) the wrong interpretation

• New interpretation based on simple-minded demographic analysis

Example 1: Comparisons of CDR across several societies

• Appearances: differences reveal health status differences

• Realities: differences are a function of differences in Mx and Cx

Example 2: Societies with equivalent trajectories in If

• Appearances: they experience same process of fertility decline

• Reality: Since If=Im*Ig, changes in If may be due to changes in Ig and/or I,m and each may depend on completely different societal forces

Example 3: The Black-White Mortality cross over

• Appearance: it reveals that Blacks have better health status at older ages

• Realities: survival of the least frail? Reporting errors? Other?

Example 4: consequences of mortality decline

• Appearance: when mortality decline, populations age

• Realities: Most of the time, mortality declines rejuvenate populations

Example 5: Aging of societies

• Appearance: It happens because populations starts having lower birth rates

• Realities: the bulk of aging in many societies has to do with mortality declines that occurred many years ago.

• Question: are this and the statement in Example 4 inconsistent?

Example No 6: The Hispanic paradox

• Appearance: Mexican immigrants appear to be blessed by better health status because of their behaviors and because of their practices

• Realities: Mexican immigrants better health status may be an artifact of their being a selected population

Example 7: The relation between births and abortions

• Appearance: one abortion averts one birth

• Reality: in non contraceptive societies, one abortion averts 1/3 of a birth. In almost perfectly contraceptive societies one abortion almost averts one birth

Approximate calculations in the absence of contraception (cc)

• When there are no abortions and no cc:– Birth interval=5(=1/.20)+9+8=22 months– Births per month=1/22=.0455*Women

• When every conception is aborted (no cc):– Birth interval=5+3=8 months– Abortions per month=1/8=.1250*Women

• Abortions---> Births (no cc):– One would need .1250*Women abortions to

prevent .0455*Women births. Or, ONE abortion prevents .1250/.0455=.3640 births

Approximate calculations when there is cc (cc)

• No abortions and 50% efficient cc– Birth interval=10(=1/(.5*.2)+9+8=27 months– Births per month=1/27=.0370*Women

• Every conception is aborted and 50% efficient cc:– Birth interval=10+3=13 months– Abortions per month=1/13=.0769*Women

• Abortions---> Births (no cc):– One would need .0769*Women abortions to

prevent .0377*women births. Or, ONE abortion prevents .0377/.0769= .49 births

Example 8: Mean age at childbearing

• Reality 1: average age at which women bear children is OLDER in societies with no contraception

• Reality 2: The average age at which women have their first, second, third, fourth, …, births is always younger in societies with no contraception

• These two statements are NOT inconsistent

Example 9: Doubling times and age distribution

• Natural rate of increase and doubling times– P(t)=P(0)*exp(rt)….r is the natural rate of increase– Td=ln 2/r…………..Td is the doubling time

• Reality I: the US has a current fertility and mortality regimes of a stationary population

• Reality II: the doubling time of the US population is of the order of 80 years

• These two statements are not inconsistent with each other: the second is also a function of age distribution

Promotion and rate of increase• Appearance: promotion has nothing to do with

population increase

• Reality: promotion depends on seniority or on one’s age relative to that of others.

• Example: Age at promotion=x

x=~ -2/3* 15* 22.5 r/100 = -2.25*r

Relation between r and economic development

• Appearance No 1: Higher rates of natural increase lead to lower rates of economic growth– Based on neoclassic growth models

• Appearance No 2: Higher rates of economic growth lead to higher rates of economic growth– Based on modified neoclassic growth models

• Resolution: too many models confronting observations

HIV/AIDS

• Appearance: SS African societies where bridal wealth is more prevalent experience higher levels of HV/AIDS

• Reality: Bridal wealth imposes constraints on age difference of spouses (pushes the average difference up). This leads to a broader diffusion of HIV/AIDS

• Main model: Stable with HIV/AIDS