Data Collection And Sampling Methods

Question 1

Outline the method for simple random sampling

Answer 1

• Each sampling unit is given a different identifying number,
• Use a random number generator on your calculator to generate the amount of random numbers needed,
• Match the chosen numbers with the corresponding sampling units.

Question 2

Give 3 advantages and 2 disadvantages of simple random sampling

Answer 2

Advantages:
- bias free
- easy and cheap to implement
- each number has a known equal chance of being selected

Disadvantages:
- not suitable with a large population, as it’s difficult to collect an accurate sampling list,
- A sampling frame is required

Question 3

Outline the method for systematic sampling

Answer 3

• Create a sampling frame,
• Each sampling unit is given an identifying number,
• K=population size/sample size
• generate a random number between 1 and k using a random number generator on your calculator,
• select the corresponding item to this number and every kth item after this, until the sample size required has been obtained

Question 4

What is systematic sampling

Answer 4

Required elements are chosen at regular intervals in an ordered list

Question 5

What is stratified sampling

Answer 5

The population is divided into groups and a simple random sample is carried out in each group

Question 6

Outline the method for stratified sampling

Answer 6

• Allocate each sampling unit in each group with a number,
• Sample the same proportion from each strata, using the formula (no.in the strata/no. In population)×sample size
• Use simple random sampling to select the units from each strata.

Question 7

What are non random sampling methods? Give 3 examples

Answer 7

These are methods when a sampling frame isn’t possible

E.g:
- Quota sampling,
- Opportunity sampling,
- Cluster sampling

Question 8

What is quota sampling

Answer 8

Sampling method where the population is divided according to characteristics

Question 9

Outline the method for quota sampling

Answer 9

• A group of sampling units in each naturally formed group (e.g. hair colour) is set to try to reflect the groups proportion in the whole population
• The interviewer selects the sampling units however they want to

Question 10

Give 2 advantages of systematic sampling

Answer 10

Simple, cheap and quick to use

Suitable for large populations

Question 11

Give 3 disadvantages for systematic sampling

Answer 11

• A sampling frame is needed which can be time consuming
• can introduce bias if the sampling frame isn’t random
• not random as not every item has an equal chance of being selected

Question 12

Give 3 advantages of stratified sampling

Answer 12

• reflects the population structure
• guarantees proportional representation of groups within population
• has random selection within an individual group to reduce bias

Question 13

Give 3 disadvantages of stratified sampling

Answer 13

• the population must be classified into distinct strata
• selection within each stratum suffers from the same disadvantages of simple random sampling, e.g. sampling frame needed and not suitable for large samples

Question 14

Give 4 advantages of quota sampling

Answer 14

• allows a small sample to still be representative of the population of that group
• no sampling frame required
• quick, easy and inexpensive
• Allows for easy comparison between different groups in the population

Question 15

Give 3 disadvantages of quota sampling

Answer 15

• non-random sampling in groups can introduce bias,
• the population must be divided into groups, which can be costly and time consuming, and inaccurate
• non -responses aren’t recorded

Question 16

What is opportunity sampling

Answer 16

The sample is taken from people who meet the criteria who are able to meet at time of study

Question 17

Give 2 advantages of opportunity sampling

Answer 17

Easy to carry out

Inexpensive

Question 18

Give 2 disadvantages of opportunity sampling

Answer 18

Unlikely to provide a representative sample

Highly dependent on individual researcher - there’s nothing from stopping them from choosing who they want to ask to get the answer they want

Question 19

Outline how to do cluster sampling

Answer 19

• split the population into relevant groups

-choose (usually randomly) some of these groups

• from these chosen groups take a sample of the required size

Question 20

What’s the difference between cluster sampling and quota sampling

Answer 20

In cluster sampling, groups are randomly selected and then the data is collected from these groups

In quota sampling, a representative proportion of each group is chosen, so at least one person is selected from each group

Question 21

Give 2 advantages of cluster sampling

Answer 21

Easy to carry out

Inexpensive

Question 22

Give 2 disadvantages of cluster sampling

Answer 22

May not be representative of whole population (things/people from the same cluster may be similar, and not every group is represented)

Non random sampling of individuals in the clusters can produce bias