Sampling Methods Flashcards
Samples selected without bias from a list of the entire target population
Random
Stratified
Systematic
Samples selected with the potential for bias
Opportunity and volunteer sampling
Random sampling strength h
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
Random sampling strength l
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
Random sampling
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
Random sampling limitation h
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
Stratified sampling strength h
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
Stratified sampling strength l
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
Random sampling limitation i
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
Stratified sampling
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
Stratified sampling limitation h
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
Systematic sampling strength h
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
Systematic sampling strength l
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
Stratified sampling limitation d
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
Systematic sampling
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)
Systematic sampling limitation h
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
Systematic sampling limitation i
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
Opportunity sampling
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
Opportunity sampling strength p
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
Opportunity sampling limitation e
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)
Opportunity sampling strength e
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
Opportunity sampling limitation l
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
Volunteer sampling
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
Volunteer sampling strength p
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
Volunteer sampling limitation h
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
Volunteer sampling strength e
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.
Volunteer sampling limitation l
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
