Sampling Methods

Question 1

Samples selected without bias from a list of the entire target population

Answer 1

Random
Stratified
Systematic

Question 2

Samples selected with the potential for bias

Answer 2

Opportunity and volunteer sampling

Question 4

Random sampling strength h

Answer 4

a strength is that it can often generate a sample with high population validity

Which is when the results can be successfully generalised to the target population, increasing the external validity of research

As each member of the target population has an equal chance of being selected, the sample is likely to be highly representative

Question 5

Random sampling strength l

Answer 5

a strength is that it has low experimenter bias

Which is when the experimenter doesn’t show unintentional bias in the selection of the participants, increasing the internal validity of research

This is because the researcher doesn’t actively choose individuals as participants are selected in an unbiased manner

Question 6

Random sampling

Answer 6

A sample generated by identifying a list of the entire target population and randomly selecting participants from this list (in an unbiased way)

The names of the entire target population can be put into a hat and drawn at random; alternatively, names could be randomly generated using a computer database

Therefore, each member of the target population has an equal chance of being selected

Question 8

Random sampling limitation h

Answer 8

Limitation is that it may not always generate a sample with high population validity

Which is extent to which results can be successfully generalised to the target population

Although the selection of participants is unbiased, the actual sample may be biased in some way if only one type of person is selected

For example, by chance only female participants may be selected from a group of males and females, meaning the sample may not be representative of the population

Question 9

Stratified sampling strength h

Answer 9

a strength is that it can often generate a sample with high population validity

Which is when the results can be successfully generalised to the target population, increasing the external validity of research

This is because an effort has been made to ensure the sample reflects the make-up of the target population, meaning the sample is likely to be highly representative

Question 10

Stratified sampling strength l

Answer 10

a strength is that it has low experimenter bias

Which is when the experimenter cannot show intentional bias in the selection of participants, increasing the internal validity of research

Although the experimenter identifies strata in the target population, he doesn’t actively choose individuals, and participants are still selected in an unbiased manner

Question 11

Random sampling limitation i

Answer 11

It is impractical,

As the full list of the target population may be difficult or impossible to obtain

For example, it may be difficult or impossible to define a complete list of all schizophrenics, meaning the sample drawn may be biased and this method cannot be used to study behaviour where no list of the target population exists

Question 12

Stratified sampling

Answer 12

A sample generated by identifying a list of the entire target population as well as the characteristics which are important to the research (e.g. gender) before randomly selecting a ration that reflects these groups (or strata)

If the target population is 40% female and 60% male, participants are drawn randomly until they reach this ratio, so the sample is representative of the structure of the target population

Question 13

Stratified sampling limitation h

Answer 13

Limitation is that it may not always generate a sample with high population validity

Which is the extent it which results can be successfully generalised to the target population

Although the selection of participants reflects the known strata of the target population, the actual sample may still be biased if only participants with can unknown characteristic are selected

Question 14

Systematic sampling strength h

Answer 14

a strength is that it can often generate a sample with high population validity

Which is when the results can be successfully generalised to the target population, increasing the external validity of research

This is because the sample will shown an unbiased representation of the target population, meaning the sample is likely to be highly representative

Question 15

Systematic sampling strength l

Answer 15

a strength is that it provides low experimenter bias

Which is when the experimenter cannot show unintentional bias in the selection of participants, increasing the internal validity of research

Although the experimenter identifies every nth person from the target population, they don’t actively choose individuals, and participants are still selected in an unbiased manner

Question 16

Stratified sampling limitation d

Answer 16

Limitation is that it is difficult and time consuming to achieve

This is because it is challenging to fully identify the characteristics of the target population that are important to the research

For example, whilst some characteristics (like gender) are easy to identify, others (like IQ) are hidden and difficult to define and this method cannot be used to study behaviour where no list of the target population exists

Question 17

Systematic sampling

Answer 17

A sample generated by identifying a list of the entire target population before specifically selecting every nth participant

For example, if there are 100 people in the target population and a sample of 20 is required, psychologists would select every 5th person from the list (100/20=5)

Question 18

Systematic sampling limitation h

Answer 18

Is that it may not always generate a sample with high population validity

Which is the extent to which results can be successfully generalised to the target population

Although the selection of participants is unbiased, the actual sample may be biased in some way if only one type of person is selected

If every nth person happens to share some characteristics (eg they all happen to be young and female), the sample may not be representative of the population

Question 19

Systematic sampling limitation i

Answer 19

It is impractical

As it still requires psychologists to devise a full list of the target population, which may be difficult of impossible to obtain

For example, it may be difficult (or impossible) to define a complete list of all schizophrenics, meaning the sample drawn may be biased and this method cannot be used to study behaviour where no list of the target population exists

Question 20

Opportunity sampling

Answer 20

A sample generated when participants take part in research based on their availability at the time of the study, often by agreeing (having been approached by the experimenter)

Here, the researcher asks available people if they are willing to take part, for example stropping people in a high street. Those who agree become the sample

Question 21

Opportunity sampling strength p

Answer 21

It is practical as it is a straightforward method that requires little time or preparation to perform

This is because the researcher simply selects participants based on their availability at the time of the research

Therefore, the method is less expensive than other methods, such as random sampling which requires significant preliminary work to be carried out

Sears (1986), found that 75% of university research uses undergraduates because of their free availability

Question 22

Opportunity sampling limitation e

Answer 22

a limitation of opportunity sampling is that is has a high level of experimenter bias

Which is when the experimenter shows unintentional bias in the selection of participants, lowering the internal validity of research

This is because the researcher directly asks people if they want to participate in the research, meaning they may show unintentional bias in their selection, by only asking certain kinds of people (eg those who look helpful)

Question 23

Opportunity sampling strength e

Answer 23

It meets the ethical guidelines of gaining general consent from participants,

Which is when they are made aware of the experimenters aims, procedures and anticipated findings before agreeing to take part in a study

This is because of the study will be described by the experimenter before they agree to take part in the experiment, allowing participants to make a more informed decision about whether to take part

Question 24

Opportunity sampling limitation l

Answer 24

Low population validity

Which is when the findings of the research cannot be generalised to the target population, decreasing the external validity of the study

This is because opportunity samples are generated when participants agree to take part, having been approached by the experimenter, meaning this sampling method may miss other groups of people who are unwilling or unable to take part in the research

Question 25

Volunteer sampling

Answer 25

A sample generated when participants self-select or volunteer to take part in research, normally in response to an advert

A psychologist may place an advert online or in a newspaper and select those who respond

Question 26

Volunteer sampling strength p

Answer 26

It is practical

As it is a straightforward method that requires little time or preparation to perform (other than producing the advert).

This is because the sample is constructed from self-selecting participants, based on their response to an advert

Therefore, the method is less expensive than other methods, such as random sampling, which requires significant preliminary work to be carried out

Question 27

Volunteer sampling limitation h

Answer 27

a limitation of volunteer sampling is that it has a high level of volunteer bias

Which may lower the internal validity of research if the volunteers have a shared personality type that acts as an extraneous or confounding variable

This is because the sample is constructed from self-selecting participants, who are likely to share similar personality traits that may not represent the target population

Question 28

Volunteer sampling strength e

Answer 28

It meets the ethical guidelines of gaining general consent from participants

Which is when they are made aware of the experimenters aims, procedures and anticipated findings before agreeing to take part in a study

This is because details of the study will be placed on the advert, allowing participants to make a more informed decision about whether to take part or not.

Question 29

Volunteer sampling limitation l

Answer 29

Has low population validity

Which is when the findings of research cannot be generalised to the target population, decreasing the external validity of the study

This is because volunteer samples are generated when participants choose to take part after responding to an advert, meaning this sample method may miss other groups of people who are unwilling or unable to take part in the research