Data Collection

Question 1

What is a census?

Answer 1

A census observed or measured every member of a population

Question 2

What is a sample?

Answer 2

A selection of observations taken from a subset of the population which is used to find out information about the population as a whole.

Question 3

Advantage of a census

Answer 3

It should give a complete accurate result.

Question 4

Disadvantages of a census

Answer 4

• Time consuming and expensive.
• Cannot be used when the testing process destroys the item.
• Hard to process a large quantity of data.

Question 5

Advantages of a sample

Answer 5

• Less time consuming and expensive than a census.
• Fewer people have to respond.
• Less data to process than in a census.

Question 6

Disadvantages of a sample

Answer 6

• The data may not be as accurate.
• The sample may not be large enough to give information about small sub-groups of the population.

Question 7

What are sampling units?

Answer 7

• Individual units of a population.
• Often sampling units of a population are individually named or numbered to form a list called a sampling frame.

Question 8

Describe simple random sampling

Answer 8

A simple random sample of size n is one where every sample of size n has an equal chance of being selected.

Question 9

Describe systematic sampling

Answer 9

The required elements are chosen at regular intervals from an ordered list.

Question 10

Describe stratified sampling

Answer 10

The population of divided into mutually exclusive strata (eg. males and females) and a random sample is taken from each.

Question 11

What are the three methods of random sampling?

Answer 11

Simple random sampling
Systematic random sampling
Stratified sampling

Question 12

Advantages of simple random sampling

Answer 12

• 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 13

Disadvantages of simple random sampling

Answer 13

• Not suitable when the population size or the sample size is large as it is potentially time consuming, disruptive and expensive.
• A sampling frame is needed.

Question 14

Advantages of systematic sampling

Answer 14

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

Question 15

Disadvantages of systematic sampling

Answer 15

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

Question 16

Advantages of stratified sampling

Answer 16

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

Question 17

Disadvantages of stratified sampling

Answer 17

• Population must be clearly classified into distinct data.
• Selection within each stratum suffers from the same disadvantages as simple random sampling (not suitable when the sample size is large, time consuming, disruptive and expensive)

Question 18

What are the two types of non-random sampling?

Answer 18

Quota sampling
Opportunity sampling

Question 19

Describe quota sampling

Answer 19

An interviewer or researcher selects a sample that reflect the characteristics of the whole population.

Question 20

Describe opportunity sampling

Answer 20

Consists of taking the sample from people who are available at the time the study is carried out and who fit the criteria you are looking for.

Question 21

Advantages of quota sampling

Answer 21

• Allows a small sample to still be representative of the whole population.
• No sampling frame required.
• Quick, easy and inexpensive.
• Allows for easy comparison between different groups within a population.

Question 22

Disadvantages of quota sampling

Answer 22

• Non-random sampling can introduce bias.
• Population must be divided into groups, which can be costly or inaccurate.
• Increasing scope of study increases number of groups, which adds time and expense.
• Non-responses are not recorded as such.

Question 23

Advantages of opportunity sampling

Answer 23

• Easy to carry out.
• Inexpensive.

Question 24

Disadvantages of opportunity sampling

Answer 24

• Unlikely to provide a representative sample.
• Highly dependent on individual researcher.