Stratified Sampling

This can only be used when there is a detailed knowledge of the population and their relative proportions
The sample is divided into non overlapping groups (or strata) based on a type of grouping (age, gender, location etc)

Advantages

1) always achieve greater accuracy the bigger the differences between the strata's the greater the precision
2) ensures better coverage of the population

Disadvantages

1) difficult to identify appropriate strata's
2) more complex to organise and analyse results