Foundational Concepts & Measures Monday, Sept 13

The Balancing Equation of Population Change Ending Population Moves Out Moves In Starting Population BirthsDeaths Natural IncreaseNet Migration

Ratios A single number expressing the relative size of two other numbers X/Y = ratio of X to Y –Examples Dependency ratio Sex ratio Population density Child-woman ratio Unemployment rate

Proportions Special type of ratio where the denominator includes the numerator –Example: Proportion of deaths that occurred to males D m D m + D f

Demographic Rates Rate = Number of Occurrences Person-Years of Exposure to the Risk of Occurrence

Person-Years Method of calculating exposure to risks –How to obtain Count them (life lines) Estimate by counting people alive at various points and weighting each count by the proportion of the year Use mid-year population

Principle Period Rates Crude Birth Rate (CBR) Crude Death Rate (CDR) Crude Rate of In-migration (CRIM) Crude Rate of Out-migration (CROM) Crude Rate of Natural Increase (CRNI) Crude Rate of Net Migration (CRNM)

Growth Rates Crude Growth Rate Linear Change Instantaneous Change –With a constant rate of change (r*) –Mean annualized growth rate (¯r) Doubling Time

Cohort Aggregate of units that experience a particular event during a specific time interval –Limitations of cohort studies Losing track of individuals/loss to follow-up By the time all info is collected, it is ancient

Probabilities The denominator is composed of all those persons in the given population at the beginning of the period of observation

Age of a Population What has more influence on the age of a population? Births or deaths? Why? Why do falling death rates make a younger population? Population pyramids