Sampling

Question 1

Simple random sampling

Answer 1

Every sample has equal chance of being selected

Question 2

Simple random sampling method

Answer 2

In sampling frame each item has identifying number. Use random number generator, or ‘lottery sampling’ (names in a hat).

Question 3

Simple random sampling method advantages

Answer 3

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

Question 4

Simple random sampling method disadvantages

Answer 4

• Not suitable when population size is large

- Sampling frame needed

Question 5

Systematic sampling

Answer 5

Required elements are chosen at regular intervals in ordererd lists e.g. every 4th element
k= pop size(N)/ samp size(n)
starting at random between 1 and k

Question 6

Systematic sampling advantages

Answer 6

• Simple and quick to use

- Suitable for large samples/populations

Question 7

Systematic sampling disadvantages

Answer 7

• Sampling frame needed

- Can introduce bias if sampling frame is not random

Question 8

Stratified sampling

Answer 8

Population divided into groups (strata) and a simple random sample carried out in each group.
Same proportion sampled from each strata
Samp size(n) / pop size (N)
Used when sample is large and population naturally divides into groups

Question 9

Stratified sampling advantages

Answer 9

• Reflects the population structure

- Guarantees proportional representation of groups within population

Question 10

Stratified sampling disadvantages

Answer 10

• Sampling frame needed
• Within the strata, the problems are the same as for any simple random sample
• Population must be clearly classified into distinct strata (no overlap)

Question 11

Quota sampling

Answer 11

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

Question 12

Quota sampling advantages

Answer 12

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

Question 13

Quota sampling disadvantages

Answer 13

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

Question 14

Opportunity sampling

Answer 14

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

Question 15

Opportunity sampling advantages

Answer 15

• Easy to carry out

- Inexpensive

Question 16

Opportunity sampling disadvantages

Answer 16

• Non random sampling can introduce bias e.g. interviewee bias
• Unlikely to provide a representative sample
• Highly dependant on individual researcher

Question 17

Cluster sampling

Answer 17

Cluster sampling is a probability sampling technique where researchers divide the population into multiple groups (clusters) for research. Researchers then select random groups with a simple random or systematic random sampling technique for data collection and data analysis.

Question 18

Population definition

Answer 18

The whole set of items that are in interest

Question 19

Sample definition

Answer 19

Some subset of the population to represent the population

Question 20

Census definition

Answer 20

A survey carried out to all items in a population

Question 21

Outlier definition

Answer 21

A point that differs significantly from the others

Question 22

Sampling frame definition

Answer 22

A list of all items to be sampled

Question 23

Sampling fraction definition

Answer 23

The proportion of the available items that are actually sampled.

Question 24

Bias definition

Answer 24

A model which is not representative of the population which is likely to include some prejudice

Question 25

Sampling error definition

Answer 25

The difference between your estimate of the parameter and the actual value

Question 26

Census advantages

Answer 26

Takes everyone opinions into account

Question 27

Census disadvantages

Answer 27

Time consuming and costly

Question 28

Cluster sampling advantages

Answer 28

• Easy to carry out

- Simple random for selecting clusters

Question 29

Cluster sampling disadvantages

Answer 29

• Differences in location

- Might not be convenient (makes sense for shops)