## Aims and objectives

### Aim

To introduce the measurement of parity progression and the duration of birth intervals from birth history data.

### Objectives

At the end of this session you should be able to:

- Explain the difference between parity progression ratios calculated for age cohorts, parity cohorts and synthetic parity cohorts
- Explain how censoring and truncation of birth history data can bias measures of parity progression and the length of birth intervals
- Calculate parity progression ratios for both true and synthetic parity cohorts
- Calculate summary measures of the length of birth intervals for both true and synthetic parity cohorts

This session will take approximately 2.5 hours to complete.