STATISTICS - Data collection

Question 1

Definition of a population

Answer 1

The whole set of items that are of interest

Question 2

Definition of a sample

Answer 2

Some subset of the population intended to represent the population

Question 3

Definition of a sampling unit

Answer 3

Each individual thing in the population that can be sampled

Question 4

Definition of a sampling frame

Answer 4

A list of all the sampling units

Question 5

Definition of a census

Answer 5

Data collected from the entire population

Question 6

Advantages of a census

Answer 6

• Should give completely accurate results
• More reliable

Question 7

Disadvantages of a census

Answer 7

• More time consuming
• More expensive
• Cannot be used when testing involves destruction
• Large volume of data to process

Question 8

Advantages of a sample

Answer 8

• Cheaper
• Quicker
• Less data to process
• Possible when data involves destruction

Question 9

Disadvantages of a sample

Answer 9

• Data may not be accurate
• Data may not be large enough to represent small sub-groups

Question 10

What is qualitative data?

Answer 10

Non - numerical values

Question 11

What is quantitative data?

Answer 11

Numerical values

Question 12

What is discrete data?

Answer 12

Can only take specific values

Question 13

What is continuous data?

Answer 13

Can take any decimal values

Question 14

What are the types of sampling?

Answer 14

Random vs Non-random sampling

Question 15

What are the 3 types of random sampling?

Answer 15

• Simple random sample
• Systematic sampling
• Stratified sampling

Question 16

What are the 2 types of non-random sampling?

Answer 16

• Quota sampling
• Opportunity sampling

Question 17

How would you carry out a simple random sample?

Answer 17

• List all members of the population and assign them a number from 1-‘n’ to each member
• Use a random number generator to select ‘k’ unique numbers (ignore repeats)
• Select the corresponding members of the population which match the numbers generated to form the sample

Question 18

Advantages of simple random sampling?

Answer 18

• Bias free
• Easy and cheap to implement
• Each number has a known equal chance of being selected

Question 19

Disadvantages of simple random sampling?

Answer 19

• Not really suitable when population size is really large
• Sampling frame needed

Question 20

How would you carry out a systematic sample?

Answer 20

• Take every Kth element where:
  > K = population size/sample size
• List all the members of the population and assign a number from 1-‘n’ to each
• Use a random number generator to select and number between 1 and K (starting point)
• Then select every Kth person to form the sample

Question 21

Advantages of systematic sampling?

Answer 21

• Simple and quick to use
• Suitable for large samples/population

Question 22

Disadvantages of systematic sampling?

Answer 22

• Sampling frame needed
• Can introduce bias if sampling frame is not random

Question 23

How would you carry out a stratified sample?

Answer 23

For each strata, calculate:
- size of strata/population size x sample size
- Carry out a simple random sample for each strata

Question 24

Advantages of stratified sampling?

Answer 24

• Reflects population structure
• Guarantees proportional representation of groups within population

Question 25

Disadvantages of stratified sampling?

Answer 25

- Population must be clearly classified into distinct data - Selection within each stratum suffers from same disadvantages as simple random sampling

Question 26

How would you carry out a quota sample?

Answer 26

- Population is divides into groups according to characteristics - A quota of items/people in each group is set to try and reflect the group's proportion in the whole population - Interviewer selects the actual sampling units

Question 27

Advantages of quota sampling?

Answer 27

- Allows small sample to still be representative of population - No sampling frame required - Quick, easy and inexpensive - Allows for easy comparison between different groups in the population

Question 28

Disadvantages of quota sampling?

Answer 28

- Non random sampling can introduce bias - Population must be divided into groups, which can be costly and inaccurate - Increasing scope of study increases number of groups, adding time/expense - Non-responses are not recorded

Question 29

How would you carry out an opportunity sample?

Answer 29

Sample taken from people who are available at time of study, who meet criteria

Question 30

Advantages of opportunity sampling?

Answer 30

- Easy to carry out - Inexpensive

Question 31

Disadvantages of opportunity sampling?

Answer 31

- Unlikely to provide a representative sample - Highly dependent on individual researcher

Question 32

Give an example of when a census would be practical and useful (PPQ)

Answer 32

A small company wishes to ask about their employee's opinions about pension schemes

Question 33

Give an example of when a census would be impractical and therefore a sample would be needed (PPQ)

Answer 33

A city council wants to find out what its residents feel about their recycling centres

Question 34

Give an example of how you could use simple random sampling to select a sample of 50 people from an alphabetical list of the 2500 inhabitants of a particular district (PPQ)

Answer 34

- Allocate each person a number starting at 1 and ending at 2500 - Use random number tables to select 50 random numbers between 1 and 2500