摘要：Revision: Age Structure There are 3 basic age structures: 1. Progressive (Brazilian) Type 2. Stationery (American) Type 3. 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 ag
Revision: Age Structure
There are 3 basic age structures:
1. Progressive (Brazilian) Type
2. Stationery (American) Type
3. 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
A-level课程优势：
· 课程体系：全程服务，20-32小时集训拔高，80小时自主学习与督导指点我们陪你每一分钟
· 课程资料：1）CIE、Edexcel官方教材；2）独家考前押题秘籍；3）2015-2017年考试真题模考精讲；
· 无忧备考：名师授课+作业批改与点评+ 期中、期末模考精讲+24小时答疑+一直到考前也会进行的伴读计划
· 明星师资：授课老师均毕业于美国TOP30名校和国内985名校，IELTS考分8+，同时教授过至少3000个小时的课程
· 教学方法：超过同类机构两倍的刷题量、考前预测各个击破讲练并进，问答结合，真正掌握每一个知识点
针对2018年的A-level考试，开设“A-level基础课程、强化课程、冲刺课程”。想快速提分的同学可以在线咨询客服，了解课程详情，预约名师1V1试听课；为你量身打造专属A-level学习方案；免费领取A-level考试学习资料/视频课件/直播公开课！