## Aims and objectives

### Aim

To introduce the basic demographic measurement tools, and to be able to calculate examples of each.

### Objectives

By the end of this session you will be able to:

- explain the difference between rates, ratios, and proportions.
- calculate rates, ratios and proportions.
- calculate and describe sex ratios, and why they are important.
- discuss the different denominators which may be used for calculating rates, and explain why demographers usually use the mid-year population.
- describe the difference between prevalence and incidence.
- explain what is meant by ‘period’ and ‘cohort’ data.
- describe the difference between a ‘real’ and a ‘synthetic’ cohort.
- draw and explain Lexis diagrams.