Sampling techniques

Question 1

Define population

Answer 1

A complete collection of relevant individual people or items.

Question 2

Define census

Answer 2

Observation or measurement of every member of a population

Question 3

Write down two disadvantages of using a census rather than a sample.

Answer 3

• takes a long time/costly
• difficult to ensure whole population surveyed
• cannot be used if the measurement process destroys the item
• can be hard to manage and analyse all the data.

Question 4

Write down two advantages of using a census rather than a sample.

Answer 4

• Unbiased
• Accuracy of the data

Question 5

What is simple random sampling

Answer 5

Each member of the population has an equal chance of being selected for the sample

Question 6

What is systematic sampling

Answer 6

Choosing from a **sampling frame. ** -If the data is numbered 1,2,3,4… randomly select the starting point and collect every nth item in the list

Question 7

What is stratified sampling

Answer 7

Ensure subgroups (strata) of a given population are each adequately represented within the whole sample population of a research study.
Sample size from each subgroup= (size of whole sample/ size of whole population) x population of subgroup

Question 8

What is quota sampling

Answer 8

Sample selected based on specific criteria e.g. age group

Question 9

What is opportunity sampling

Answer 9

E.g. the first 5 people who enter a leisure centre or teachers in a single primary school surveryed to find infomation about working in primary education across the UK

Question 10

A sixth form college has 84 students in Year 12 and 56 students in Year 13
The head teacher selects a stratified sample of 40 students, stratified by year group.
(a) Describe how this sample could be taken.

Answer 10

• He could get a register of Year 12s
• Assign each pupil a number
• Use a random number generator to pick 24
• Repeat for Year 13s (to pick 16 year 13s)

Question 11

Disadvanatges of systematic sampling

Answer 11

• not random
• random number generator may have errors
• there may not be enough – on the random number generator

Question 12

Advantages of quota sampling

Answer 12

• easy to get sample size
• inexpensive
• fast
• can be stratified if required.

Question 13

Disadvantages of quota sampling

Answer 13

• Not random
• Can be biased

Question 14

2 marks

Graham has an equivalent list of 300 females.
Explain how Graham could take a systematic sample of blood from 50 females aged 25 to 35

Answer 14

Use a random number generator to select the first name as a starting point and then select
every 6th name thereafter to get 50 names.

Question 15

3 marks

Graham then decides to select the 50 male blood samples from an alphabetical list of 300 names
of males aged 25 to 35, each of whom has agreed to supply a sample if asked.
Explain how Graham could use a calculator or a random number generator to take a simple
random sample from the males aged 25 to 35.

Answer 15

Allocate each of the males a number from 1 to 300
Use calculator or number generator to generate 50 different random numbers from 1 to 300 inclusive.
Select males corresponding to those numbers.