1.3 Non-Random Sampling Methods

Describe quota sampling

Similar to stratified sampling in that the population is divided into sub-groups according to particular criteria. The size of each sub-group determines the proportion of the sample that should meet each criteria. Once each sample element is selected it is assigned to an appropriate quota. Once a quota is full, any further sampling elements which would fit the quota are ignored. Sampling elements continue to be chosen until all quotas are full

Describe opportunity sampling

Sampling elements are chosen from those that are available at the time the study is carried out and which fit the criteria being studied.

What is opportunity sampling sometimes called?

Convenience sampling

Advantages of quota sampling

• Allows a small sample to still be representative of the population

• No sampling frame required

• Quick, easy and inexpensive

• Allows for easy comparison between different groups within a population

Disadvantages of quota sampling

• Non-random sampling can introduce bias

• Population must be divided into groups, which can be costly or inaccurate

• Increasing scope of study increases number of groups, which adds time and expense

Advantages of opportunity sampling

• Easy to carry out

• Inexpensive

Disadvantages of opportunity sampling

• Unlikely to provide a representative sample

• Highly dependent on individual researcher