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
