Sampling methods

Population

The whole set of items of interest

Census

All items from the population are observed/measured

Sample

A subset of the population is observed/measured

Sampling frame

A complete list of the entire population that is individually named or numbered

Random sampling

Each member of the population has an equal chance of being selected

Give 2 advantages and 2 disadvantages of simple random sampling

Advantages

• Free of bias

• Easy and cheap for small samples and populations

Disadvantages

• Not suitable for large samples and populations

• Sampling frame needed

Give 2 advantages and 2 disadvantages of systematic sampling

Advantages

• Simple and quick to use

• Suitable for large samples and large populations

Disadvantages

• Bias introduced if sampling frame is not random

• Sampling frame needed

Give 2 advantages and 2 disadvantages of stratified sampling

Advantages

• Sample accurately reflects population structure

• Ensures no groups are under/over represented

Disadvantages

• Population must be clearly classified into distinct strata

• Same disadvantages as simple random sampling within each stratum (e.g: sampling frame needed)

Give an advantage and 2 disadvantages of opportunity sampling

Advantage

• Easy and inexpensive

Disadvantages

• Unlikely to provide a representative result

• Highly dependent on individual researcher (researcher can create bias)

Give an 3 advantages and 2 disadvantages of quota sampling

Advantages

• Easy and inexpensive

• No sampling frame required

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

Disadvantages

• Non-random sampling can introduce bias

• Population must be divided into groups, this can be innacurate

What are the 3 types of random sampling?

• Simple random sampling

• Systematic sampling

• Stratified sampling

What are the 2 types of non-random sampling?

• Quota sampling

• Opportunity/convenience sampling