Foundational Concepts & Measures

Monday, Sept 13

The Balancing Equation of Population Change

EndingPopulation

MovesOut

MovesIn

StartingPopulation

Births Deaths

Natural Increase Net 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

Dm

-------------------

Dm + Df

Demographic Rates

Rate =

Number of Occurrences

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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