TSR Wiki > Study Help > Subjects and Revision > Revision Notes > Geography > Age Structure
There are 3 basic age structures:
- Progressive (Brazilian) Type
- Stationery (American) Type
- Regressive (European) Type
Progressive Type
- It has a wide base that quickly narrows upwards to a point.
- It indicates a large birth rate, but poor conditions mean people rapidly die off, hence the triangular shape of the structure. The population is increasing.
Stationery Type
- The shape of this structure is more "square." All age groups are well represented.
- It indicates that the birth rate is moderate, and few people die off as they get older. The population is stagnant.
Regressive Type
- The structure has a fairly wide top with a bulging middle and narrow base.
- The birth rate is low, hence the low base, and there are more adults than children. The population is decreasing.
The Dependency Ratio
- This is the ratio between the non-working population (children and aged) and the workers (adults).
- It is lowest in regressive populations and highest in progressive populations.
- It is calculated using the formula (children + aged)/Adults) * 100
- In developed countries, the DRs range from 50-70. In most developing countries the DRs are over 100
The Old Age Index
- This is the proportion of aged to adults.
- It is calculated using the formula: (aged)/(adults) * 100
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