Population

The whole group of items of interest

Census

A survey of the whole population

Sample

A subset of the whole population

Sampling Unit

Each individual member of a population

Sampling Frame

A named or numbered list of all the members of the population

Random Sampling

A sampling method where every member of the population has an equal chance of being selected

Non-random Sampling

A sampling method that is not random, some members of the population have more chance of being selected

What are the different types of random sampling?

- Simple random
- Systematic sampling
- Stratified sampling

What are the different types of non-random sampling?

- Quota sampling

- Opportunity sampling

What are the advantages of simple random sampling?

- Bias free
- Easy and cheap
- Each member has an equal chance of being selected

What are the disadvantages of simple random sampling?

- Sampling frame needed
- Not suitable for large population
- Time consuming and expensive for large population
- Missing values in data

What are the advantages of systematic sampling?

- Simple and quick to use
- Unbiased and representative
- Good for large samples / populations

What are the disadvantages of systematic sampling?

- Sampling frame needed
- Introduce bias if sampling frame not random
- Missing values in data

What are the advantages of stratified sampling?

- Accurately reflects population structure
- Proportional representation of groups within population
- Random selection within each strata

What are the disadvantages of stratified sampling?

- Sampling frame needed

- Population must be classified into clear strata

What are the advantages of quota sampling?

- Sample is representative of population
- No sampling frame needed
- Quick, easy and inexpensive

What are the disadvantages of quota sampling?

- Introduce bias
- Population must be divided into groups = costly
- Increase scope of study = increase groups = increase cost
- Non-responses aren’t recorded

What are the advantages of opportunity sampling?

- Easy to carry out

- Inexpensive

What are the disadvantages of opportunity sampling?

- Introduce bias

- Dependent on individual researcher