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This lesson explores how populations are structured by age and sex, the concept of dependency, and the causes, patterns, and consequences of migration. You will study key theoretical frameworks including Ravenstein's Laws of Migration (1885) and Lee's Push-Pull Model (1966), alongside contemporary case studies from the UK and globally.
The age-sex structure of a population describes the proportion of people in different age groups, divided by sex. It is typically represented using a population pyramid.
Key Definition: The dependency ratio measures the proportion of the population that is economically dependent (too young or too old to work) relative to the working-age population.
| Measure | Formula | Interpretation |
|---|---|---|
| Total Dependency Ratio | ((0–14 age group + 65+ age group) / 15–64 age group) × 100 | Higher values mean more dependants per worker |
| Youth Dependency Ratio | (0–14 age group / 15–64 age group) × 100 | High in Stage 2/3 DTM countries |
| Old-Age Dependency Ratio | (65+ age group / 15–64 age group) × 100 | High in Stage 4/5 DTM countries |
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