Sampling

Question 1

Define a census?

Answer 1

Measures every member of the population

Question 2

Advantages of a census

Answer 2

1) It should give a completely accurate result

Question 3

Disadvantages of a census

Answer 3

1) Time consuming & expensive
2) Cannot be used when the testing process destroys the item
3) Hard to process large quantity of data

Question 4

Define a sample

Answer 4

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 5

Advantages of a sample

Answer 5

1) Less time consuming & expensive than a census
2) Fewer people have to respond
3) Less data to process than in a census

Question 6

Disadvantages of a sample

Answer 6

1) The data may not be as accurate

2) The sample may not be large enough to give information about small sub-groups of the population

Question 7

Define sampling unit

Answer 7

Individual units of a population.

Question 8

Define sampling frame

Answer 8

Sampling units given a name or number and compiled into a list

Question 9

Define quantitative data

Answer 9

You can associate data with numerical observations

Question 10

Define qualitative data

Answer 10

Associate data with non-numerical observations

Question 11

Summarise simple random sampling

Answer 11

Every sample of size n has an equal chance of being selected

Question 13

Describe how simple random sampling is conducted

Answer 13

1) Create a sampling frame

2) Pick each sample by lottery or random number generator

Question 14

Advantages of simple random sampling

Answer 14

1) Free of bias
2) Easy and cheap to implement for small populations & small samples
3) Each sampling unit has a known and equal chance of selection

Question 15

Summarise systematic random sampling

Answer 15

Required elements are chosen at regular intervals from an ordered list

Question 16

Disadvantages of simple random sampling

Answer 16

1) Not suitable when the population size or the sample size is large
2) A sampling frame is needed

Question 18

Describe how systematic random sampling is conducted

Answer 18

1) Create an ordered list
2) If sample of 20 required from 100, divide 100 by 20 = 5
3) Starting at any random number, record that first then every 5th value e.g 2, 7, 12

Question 19

Summarise stratified random sampling

Answer 19

Population divided into mutually exclusive strata (e.g males and females) and a simple random sample is taken from each

Question 20

Describe how you conduct stratified random sampling

Answer 20

1) Divide population into mutually exclusive strata
2) Keep proportion the same by: number in strata/number in population x sample size
3) Round to nearest whole number
4) Perform simple random sampling

Question 21

Advantages of stratified random sampling

Answer 21

1) Sample accuracy reflects the population structure

2) Guarantees proportional representation of groups within a population

Question 22

Disadvantages of stratified random sampling

Answer 22

1) population must be clearly classified into distinct strata
2) Selection within each stratum suffers from the same disadvantages as simple random sampling

Question 23

Summarise the non-random sampling, Quota sampling

Answer 23

An interviewer/researcher select a sample that reflects the characteristics of the whole population

Question 24

Describe how the non random sampling, Quota sampling, is conducted

Answer 24

1) Design characteristic groups and divide population into these groups
2) Interview each person and assess which group they fall into
3) Size of each group determines proportion of the sample that should have that characteristic
4) Stop interviewing when quota field. People who refuse to be interviewed are ignored, move onto next person

Question 25

Advantages of the non-random sampling, quota sampling

Answer 25

1) Allows a small sample to still be representative of the population
2) No sampling frame required
3) Quick, easy, inexpensive
4) Allows for easy comparison between different groups within the population

Question 26

Disadvantages of the non random sampling, quota sampling

Answer 26

1) Non-random sampling can introduce bias
2) Population divided into groups which is costly or inaccurate
3) Increasing scope of study increases number of groups, adding time and cost
4) Non-responses are not recorded

Question 27

Summarise the non random sampling, opportunity sampling

Answer 27

Taking a sample of people who are available at the time and fit the criteria you are looking for

Question 28

Describe how the non random sampling, opportunity sampling, is conducted

Answer 28

E.G pick the first 20 people you meet outside a supermarket on a Monday morning

Question 29

Advantages of the non-random sampling, opportunity sampling

Answer 29

1) Easy to carry out

2) Inexpensive

Question 30

Disadvantages of the non random sampling, opportunity sampling

Answer 30

1) Unlikely to provide a representative sample

2) Highly dependent on individual researcher

Question 31

Advantages of systematic random sampling

Answer 31

1) Simple & quick to use

2) Suitable for large samples and large populations

Question 32

Disadvantages of systematic random sampling

Answer 32

1) A sampling frame in needed

2) It can introduce bias if the sampling frame is not random