1.3 non-random sampling, 1.4 types of data

What are two types of non-random sampling we need to know?

• Quota sampling

• Opportunity sampling

What is quota sampling?

An interviewer or researcher selects a sample that reflects the characteristics of the whole population

How is stratified sampling carried out?

• The population is divided into groups according to a given characteristic

• The size of each group determines the proportion of the sample that should have that characteristic

• As an interviewer, you would meet people, assess their group and then, after interview, allocate them into the appropriate quota

• This continues until all quotas have been filled

• If a person refuses to be interviewed or the quota into which they fit is full, then you simply ignore them and move on to the next person

What is opportunity sampling?

Consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for

What is opportunity sampling sometimes called?

Convenience sampling

How would opportunity sampling be carried out?

For example, this could be the first 20 people you meet outside a supermarket on a Monday morning who are carrying shopping bags

What are 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

What are 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

• Non-responses are not recorded as such

What are advantages of opportunity sampling?

• Easy to carry out

• Inexpensive

What are disadvantages of opportunity sampling?

• Unlikely to provide a representative sample

• Highly dependent on individual researcher