Sampling Techniques

Question 1

What is a population?

Answer 1

The whole set of items of interest

Question 2

What is a census?

Answer 2

An observation or measurement of every member of a population

Question 3

What is a sample?

Answer 3

A selection of observations taken from a subset of the population, representing the population as a whole

Question 4

Advantages and disadvantages of a census?

Answer 4

• Gives a completely accurate result
  However:
• Time consuming and expensive
• Cannot be used when the testing destroys the item
• Hard to process large quantities of data

Question 5

Advantages and disadvantages of a sample?

Answer 5

• Less time consuming and expensive
• Less people have to respond
• Less data to process
  However:
• Data may not be as accurate
• Sample may not be large enough to give information about sub groups of the population

Question 6

What is a sampling unit?

Answer 6

An individual member of the population

Question 7

What is a sampling frame?

Answer 7

An ordered list of all the sampling units

Question 8

What is simple random sampling?

Answer 8

Each sample unit has an equal chance of being selected using a method such as a hat or random number generator

Question 9

What is systematic sampling?

Answer 9

The required elements are chosen at intervals from an ordered list (sampling frame)

Question 10

What is stratified sampling?

Answer 10

The population is divided into mutually exclusive strata, and a random sample is taken from each

Question 11

Advantages and disadvantages of a simple random sample?

Answer 11

• Free of bias
• Easy and cheap for small populations and small samples
• Each sampling unit has an equal chance of selection
  However:
• Can be time consuming, disruptive and expensive for a large sample size
• A sampling frame is needed

Question 12

Advantages and disadvantages of a systematic sample?

Answer 12

• Simple and quick
• Suitable for large samples and populations
  However:
• Can introduce bias if the sampling frame is not random
• A sampling frame is needed

Question 13

Advantages and disadvantages of a stratified sample?

Answer 13

• Accurately reflects population structure
• Guarantees proportional representation of groups
  However:
• Population must be clearly classified into strata
• Selection within each stratum suffers from the disadvantages simple random sampling

Question 14

What is quota sampling?

Answer 14

An interviewer or researcher selects a sample that reflects the characteristics of the whole population, and each person is observed

Question 15

What is opportunity sampling?

Answer 15

A sample is taken from the people who are available at the time of the study and who fit the criteria you are looking for

Question 16

Advantages and disadvantages of a quota sample?

Answer 16

• Allows a small sample to be representative of the population
• No sampling frame required
• Quick, easy and inexpensive
• Allows for easy comparison between groups
  However:
• Non random sampling can introduce bias
• Population must be divided into groups, which can be costly or inaccurate
• Increasing the scope of the study increases groups, therefore time and expense
• Non responses are not recorded as such

Question 17

Advantages and disadvantages of an opportunity sample?

Answer 17

• Easy to carry out
• Inexpensive
  However:
• Unlikely to provide a representative sample
• Highly dependent of the individual researcher

Question 18

How do you calculate the number of samples to take per stratum in a stratified sample?

Answer 18

(Number in stratum/number in population) * overall sample size