Central Role of CompositionSociology 674, 9/22/05, page 1Central Role of Composition1) Crude rates heavily influenced by composition of populationa. Especially true of death rates2) Substantive importance of compositiona. Policy implicationsb. Implications for growth (momentum) 3) Main focus of applied demographic research a. market researchb. local govt. planningSociology 674, 9/22/05, page 2Basic measures of population composition1) Population pyramids2) Sex ratios3) Aging index, dependency ratios4) Mean age, etc.5) Typically from census data6) Measurement error – reviewa. Heaping, digit preference, misreportingb. Whipple’s index, studies of AA-W “crossover”Sociology 674, 9/22/05, page 3Reciprocal influences of vital rates and populationage composition1) Births and deaths (and migrations) do not occur with equal probability for all people2) Current (and future) age composition reflect past trends in vital ratesa. Baby booms, fertility decline, famine, war, immigration, etc. (China as an extreme ex.)b. How does a population get older?3) Current age composition will influence future vital ratesSociology 674, 9/22/05, page 4Typical age patterns1) High fertility – rapid growth2) Fertility decline3) Low fertility – stable population4) Theoretically stable population in long-run5) Persistency of age structurea. population momentumb. change in infant mortality and fertilityc. implications for projectionsSociology 674, 9/22/05, page 5Sex Ratio1) (M ÷ F) x 1002) 105 at birth normally 3) Can be very low at older ages4) Relevance for marriage, etc.a. Marriage squeeze5) Determined bya. Sex ratio at birthb. Sex differences in mortalityc. Sex differences in migrationSociology 674, 9/22/05, page 6Other measures of age structure1) Aging index = (P65+÷P) x 100a. Monaco 22, Japan 20b. UAE 1, African countries 22) Proportion children = (P15÷P) x 100a. Uganda 51, Monaco 13, Japan 143) Dependency ratio [(P0-14+P65+)÷P15-64] x 1004) Old age dependency ratio5) Child dependency ratioSociology 674, 9/22/05, page 7Impact of composition on crude rates1) CDR= (D ÷ P) * 1,0002)000,1*PP*PDCDRx1000xxx3) CDR is a function of mortality levels and population
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