Chapter 1 Sampling - Year 1

Question 1

What is a population?

Answer 1

A population consists of all the items that we are interested in

Question 2

What is a sample?

Answer 2

A sample is a subset of items chosen from a population

Question 3

What is a sampling unit?

Answer 3

Each individual item in the population that can be sampled

Question 4

What is the sampling frame?

Answer 4

Sampling units of a population are individually named or numbered to form a list called the sampling frame

Question 5

What is a census?

Answer 5

When information about the entire population is measured

Question 6

What is a sample?

Answer 6

A small selection of the population

Question 7

What are the advantages of a census?

Answer 7

It is completely accurate

Question 8

What are the disadvantages of a census?

Answer 8

Time consuming
Expensive
Can’t be used when testing involves destruction
There are large volumes of data to proses (impractical)

Question 9

What are advantages of a sample?

Answer 9

Less expensive
Less time consuming
Less data to process (more practical)

Question 10

What are the disadvantage of a sample?

Answer 10

Data may not be accurate
Sample may be too small to be represent small sub-groups of the population

Question 11

What are the different ways of random sampling?

Answer 11

Simple random
Systematic sampling
Stratified sampling

Question 12

Explain how you would do a simple random sample

Answer 12

Allocate a number between 1 and x to each pupil
Use a random number generator to select y about of numbers
The students corresponding to those numbers become the sample

The assigning people numbers may have already be done for you in the question you would need to say use the … eg odifjcjfmekwoeodkdkdkdk

Q1

Question 13

Explain how you would do a systematic sample

Answer 13

Population ÷ sample wanted = z

Assign each person a random number between 1 and y
Randomly select a number between 1 and z as a starting point
Then select that person and every zth person after that

The assigning people numbers may have already be done for you in the question you would need to say use the … eg odifjcjfmekwoeodkdkdkdk

Q2

Question 14

Explain how you would do a stratified sample?

Answer 14

First you work out the number of people you will sample of each group

(Sample ÷ total) X size of stratified sample
(Sample ÷ total) X size of stratified sample
…

Explain how you would sample inside each group. If the question doesn’t say use simple random sample as it is easier. Make sure to be using exact info. Eg from the class register. Number 1 - y. Random number generator

Question 15

How could you randomly select people without a random number generator?

Answer 15

Rolling a dice

Question 16

What are the advantages of using a simple random sample?

Answer 16

Bias free
Easy
Cheap

Question 17

What are the disadvantages of simple random sample?

Answer 17

Not suitable when the population size is large as smaller minority groups may be missed
May not be an accurate representation of the population
A sampling frame is needed

Question 18

What are the advantages of systematic sampling?

Answer 18

Simple
Quick
Suitable for large samples and populations

Question 19

What are the disadvantages of systematic sampling?

Answer 19

Can introduce bias if the sample is too small and patters emerge
A sampling frame is needed

Question 20

What is a strata?

Answer 20

When you divide the populations in different groups

Question 21

What are the advantages of stratified sampling?

Answer 21

Sample accurately reflects population structure
Guarantees proportional representation between different groups

Question 22

What are the disadvantage of stratified sampling?

Answer 22

Sample frame is needed
Population must be clearly separated into different strata
Selection from each stratum is subjected to disadvantages from simple and systematic sampling

Question 23

What is Quota sampling?

Answer 23

When the population is divided into different groups according to different characteristics so that a population is represented
Interviews then select the sampling unit until the quota is filled

Question 24

What are the advantages of quota sampling?

Answer 24

Allows a small sample to be representative of a population
No sampling frame reauired
Relatively quick
Easy
Inexpensive

Question 25

What are the disadvantages of quota sampling?

Answer 25

Non random sampling can introduce bias
There needs to be clear groups
The different groups may be not easily defined or rude

Question 26

What types of sampling are non random?

Answer 26

Quota sampling
Opportunity sampling

Question 27

What is opportunity sampling?

Answer 27

A sample taken from the people who are available at the time who need the criteria

Question 28

What are the advantages of opportunity sampling?

Answer 28

Easy to do
Cheap

Question 29

What are the disadvantages of opportunity sampling?

Answer 29

Unlikely to provide a representative sample

It is dependent on the researcher

Question 30

Why may a random sample not be able to be used?

Answer 30

A sampling frame can’t be created

Question 31

How do you do a opportunity sample?

Answer 31

You stand outside a place and you interview the first people who come buy who meet your criteria

Question 32

How do you do a quota sample?

Answer 32

You need to calculate how big each quota is. Use the formula ((n.population ÷ Total population) X n.sample)

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Question 33

What is the difference between stratified and quota sampling?

Answer 33

In a stratified sample the people selected within each strata are randomly selected but in a quota sample the sample will be the first n people who the researcher meets