Sampling Methods

Question 1

What is the population?

Give an example

Answer 1

POPULATION – the large group of individuals that a particular research may be interested in studying.

Examples: Students attending colleges in Leeds, children under six with autism, women in their thirties, etc.

Often called the target population because it is a subset of the general population.

Question 2

What is the target population?

Answer 2

a group of people a researcher is interested in. E.g., looking at whether videogames make children violent, the target population is children

Question 3

What is sampling?

Answer 3

the process of selecting a representative group from the population under study.

Question 4

Why does the researcher take a representative sample?

Answer 4

Not EVERYONE in the target population can/will be used, so a researcher needs to take a REPRESENTATIVE SAMPLE so they can generalise to people who make up the target population.

Question 5

What is a biased sample?

Give an example

Answer 5

Biased sample is when certain groups are over or underrepresented within the sample selected.

For instance, if only males are selected, or if the advert for volunteers is put into the Guardian, only people who read the Guardian are selected.

This limits how much the findings of the study can be generalised to the whole population.

Question 6

What is generalisability?

Answer 6

Generalisability refers to the extent to which we can apply the findings of our research to the target population we are interested in. This can only occur if the sample of participants is representative of the population.

Question 7

What sample is most representative of target population?

What problems is there with this?

Answer 7

The larger your sample, the more representative it is of the target population

Large samples aren’t always practical (time, money etc.)

There are various ways to select participants for your sample…

Question 8

What are the different types of sampling

Answer 8

Random
Volunteer
Stratified
Systematic
Opportunity

Question 9

What is random sampling?

Answer 9

a type of probability sampling where everyone in the entire target population has an equal chance of being selected.

Question 10

How is random sampling carried out?

Answer 10

A complete list of all the members of the target population is obtained. All names on the list are assigned a number then the sample is generated using some lottery method. E.g., computer-based randomiser or picking numbers from a hat.

Question 11

Weaknesses of random sampling

Answer 11

Difficult to do when the target population is large and not all members are available/wish to take part (time, effort & money).

Question 12

Strengths of random sampling

Answer 12

The sample should represent the target population and eliminate sampling bias.

Question 13

What is opportunity sampling?

Answer 13

The use of people from target population available at the time and willing to take part. It is based on convenience.

Question 14

How is opportunity sampling carried out?

Answer 14

The researcher simply takes the chance to ask whoever is around at the time of their study.

E.g., in the street (as in market research)

Question 15

Strengths of opportunity sampling

Answer 15

Quick and easy way of choosing participants (saving time, money and effort).

Question 16

Weaknesses of opportunity sampling

Answer 16

It may not provide a representative sample of the target population and could be biased. As samples are usually drawn from one area like a street in one town which cannot be generalise.

Question 17

What is systematic sampling?

Answer 17

Chooses subjects in a systematic (i.e., orderly / logical) way from the target population, like every nth participant on a list of names.

E.g., every 3rd house on a street or every 5th pupil on a school register.

Question 18

How is systematic sampling carried out?

Answer 18

A sampling frame is produced, which is a list of people in the target population organised into, for instance alphabetical order.

A sampling system is nominated (every 3rd, 6th or 8th person, etc) or randomly determining the interval to reduce order bias.

Question 19

Weaknesses of systematic sampling

Answer 19

Difficult to achieve due to time, effort and money.

Question 20

Strengths of systematic sampling

Answer 20

Avoids research bias as the researcher has no influence on who is chosen once the system for selection has been established (even more so when if the system is randomised).

Representative as it would be possible but unlikely to get an all-male sample through this sampling.

Question 21

What is volunteer sampling?

Answer 21

a sampling technique where participants self-select to become part of a study because they volunteer when asked, or respond to an advert

Question 22

How is volunteer sampling carried out?

Answer 22

The research places an advert and people respond by going to the researcher.

Question 23

Weaknesses of volunteer sampling

Answer 23

Often unrepresentative of the target population so difficult to generalise results

Volunteer bias – Asking for volunteers may attract a certain ‘profile’ of person (e.g., more motivated) which will affect generalisability of findings.

Question 24

Strengths of volunteer sampling

Answer 24

Easy and convenient

Likely to result in large samples

Question 25

What is stratified sampling?

Answer 25

The researcher identifies the different types of people that make up the target population and works out the proportions needed for the sample to be representative.

Question 26

How is stratified sampling carried out?

Answer 26

Researcher first identifies the different strata that make up the population then the proportions needed for the sample to be representative are workout. The participants that make up each stratum are selected using random sampling. E.g., In Manchester, 40% of people support Man U, 40% support Man City, 15% support Bolton and 5% support Leeds.

Question 27

Weaknesses of stratified sampling

Answer 27

The identified strata may not reflect all the ways that people are different, therefore, complete representation is not possible. Difficult and time consuming.

Question 28

Strengths of stratified sampling

Answer 28

Research bias avoided due to once the target population has been sub-divided into strata, the participants that make up the numbers are randomly selected and out of the researcher's control. Representative – designed to accurately reflect the nature of the population and can be generalised.

Question 29

Stratified sample Example & Explained

Answer 29

Example: An occupational psychologists wishes to find out how the employees in a firm feel about new proposals for important reorganisation with the firm. This firm consists of five departments: Shop-floor workers = 60% of the workforce Supervisors = 10% of the workforce Office staff = 20% of the workforce Buyers = 6% of the workforce Management = 4% of the workforce The total number of employees is approximately 1,000. the psychologists decides to use a sample of 50. Calculate the percentages of each strata (department) – e.g., 10% of 1,000 = 100 = supervisors Number of stratum/population size x sample size = stratum size (100/1,000 x 50 = 5) Repeat step 1 & 2 for the rest of the stratums

Question 30

Study tips

Answer 30

Don’t confuse opportunity sampling and random sampling. If the word is used in its everyday sense, it could be argued that opportunity sampling involves selecting people ‘at random’. In Psychology, however, random sampling is a much more sophisticated and complex process.