random sampling 1.2

Question 1

Name the three methods of random sampling

Answer 1

• Simple random sampling
• Systematic sampling
• *Stratified sampling

Question 2

How to carry out: Simple random sampling

Answer 2

• every sample has an equal chance of being selected
• in a sampling frame, each item has an identifying number. Use random number generator or ‘lottery sampling’

Question 3

Advantages of simple random sampling

Answer 3

• Free of bias
• Easy and cheap to implement for small
  populations and small samples
• Each sampling unit has a known and equal chance of selection

Question 4

Disadvantages of simple random sampling

Answer 4

*Not suitable when the population size or the sample size is large
* A sampling frame is needed

Question 5

How to carry out: Systematic Sampling

Answer 5

• Required elements are chosen at regular intervals in ordered list
• Population size (N) / Sample size (n)
  –> starting at random item between 1 and K

Question 6

Advantages of Systematic Sampling

Answer 6

• Simple and quick to use
• Suitable for large samples and large populations

Question 7

Disadvantages of Systematic sampling

Answer 7

• A sampling frame is needed
• It can introduce bias if the sampling frame is not random

Question 8

How to carry out: Stratified sampling

Answer 8

• Population is divided into groups and a simple random sample carried out in each group
• Sample size (n) / population size (N)

—> used when sample is large

Question 9

Advantages of stratified sampling

Answer 9

*Sample accurately reflects the population structure
*Guarantees proportional representation of groups within a population

Question 10

Disadvantages of stratified sampling

Answer 10

*Population must be clearly classified into distinct strata
* Selection within each stratum suffers from
the same disadvantages as simple random sampling