Unit 1- Statistical Sampling

Question 1

Population

Answer 1

The whole set of items that are of interest

Question 2

Census

Answer 2

Observes or measures every member of a population

Question 3

Sample

Answer 3

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

Question 4

Sampling units

Answer 4

Individual units of a population (often individually named/numbered)

Question 5

Sampling frame

Answer 5

A list of sampling units

Question 6

Advantage(s) of a census

Answer 6

Should give a completely accurate result

Question 7

Disadvantage(s) of a census

Answer 7

• Time-consuming and expensive
• Can’t be used when testing destroys the item
• Hard to process if a large quantity

Question 8

Advantages(s) of a sample

Answer 8

• Less time-consuming and expensive
• Fewer people are needed
• Less data to process

Question 9

Disadvantage(s) of a sample

Answer 9

• Data may not be as accurate
• Not enough sample to inform about small sub-groups of the population

Question 10

Random sampling

Answer 10

Every member of the population has an equal chance of being selected, so the sample would be representative of the population

Question 11

Three methods of random sampling

Answer 11

Simple random sampling, systematic sampling and stratified sampling

Question 12

Simple random sampling

Answer 12

Allocate each person or thing a unique number and then randomly generate using a random number table or lottery sampling

Question 13

Lottery sampling

Answer 13

The members of the sampling frame could be written on tickets and placed into a ‘hat’

Question 14

Systematic sampling

Answer 14

The required elements are chosen at random intervals from an ordered list

Question 15

Stratified sampling

Answer 15

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

Question 16

The number sampled in a stratum =

Answer 16

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

Question 17

Advantage(s) of random sampling

Answer 17

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

Question 18

Disadvantage(s) of random sampling

Answer 18

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

Question 19

Advantage(s) of systematic sampling

Answer 19

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

Question 20

Disadvantage(s) of systematic sampling

Answer 20

• A sampling frame is needed
• Can introduce bias if the sampling frame is random

Question 21

Advantage(s) of stratified sampling

Answer 21

• Sample accurately reflects the population structure
• Guarantees proportional presentation of groups in a population

Question 22

Disadvantage(s) of stratified sampling

Answer 22

• Population must be clearly classified into distinct strata
• A sampling frame is needed
• Not suitable when the population/sample size is to large

Question 23

Two methods of non-random sampling

Answer 23

Quota sampling and opportunity sampling

Question 24

Quota sampling

Answer 24

An interview selects a sample that reflects the characteristics of a wide population and allocates them into an appropriate quota

Question 25

Opportunity sampling

Answer 25

Taking the sample from people who are available at the time the study is carried out and who fit the required criteria

Question 26

Advantage(s) of quota sampling

Answer 26

• Allows a small sample to still be representative
• No sampling frame needed
• Quick, easy and cheap
• Easy to compare between different groups

Question 27

Disadvantage(s) of quota sampling

Answer 27

• Can introduce bias
• Population must be divided into groups which can be costly or inaccurate
• Increasing scope of study increases number of groups, increasing time and expense
• Non-responses aren’t recorded as such

Question 28

Advantage(s) of opportunity sampling

Answer 28

• Easy to carry out
• Inexpensive

Question 29

Disadvantage(s) of opportunity sampling

Answer 29

• Unlikely to be representative
• Dependant on each researcher

Question 30

Quantitative data/variables

Answer 30

Associated with numerical observations

Question 31

Qualitative data/variables

Answer 31

Associated with non-numerical observations

Question 32

Continuous variable

Answer 32

Can take any value in a given range

Question 33

Discrete variable

Answer 33

Can only take specific values in a given range

Question 34

Class boundaries in a group frequency table

Answer 34

The maximum and minimum values in each class

Question 35

Midpoint in a group frequency table

Answer 35

The average of the class boundaries

Question 36

Class width in a group frequency table

Answer 36

The range of the class boundaries