sampling Flashcards
what does population refer to?
Refers to the large group of individuals that a particular researcher may be interested in studying
what does target population refer to?
Refers to a particular subset of the overall population from which the sample will be taken
what does sample refer to?
Refers to the group of people who take part in a research investigation. It is drawn from the target population and is presumed to be representative of that population
what does bias refer to?
When certain groups may be over- or under-represented within the sample selected. This limits the extent to which generalisations can be made to the target population.
what does generalisation refer to?
The extent to which findings and conclusions can be broadly applied to the population. This is made possible if the sample of participants is representative of the population.
what does representative refer to?
In relation to sampling, this means that the sample contains the same characteristics as the target population from which it was taken.
what are the 5 sampling methods called?
-random
-systematic
-stratified
-opportunity
-volunteer
how does random sampling work?
-Each member of a population has an equal chance of being selected.
- A list of all members of the target population is obtained. · All the names on the list are assigned a number. ·
-The sample is generated using some sort of lottery method (random number generator or picking names out of a hat).
what are the strengths of random sampling?
Potentially unbiased.
This means that confounding or extraneous variables should be equally divided between the different groups, enhancing internal validity.
-It is difficult and time consuming to conduct. A complete list of the target population may be extremely difficult to obtain.
- The sample may still be unrepresentative. The laws of probability suggest that random sampling is likely to produce a more representative sample than opportunity sampling. However, it is possible that the random method may select for example one particular strata.
-Selected participants may refuse to take part.
how does systematic sampling work?
-Every nth member of the target population is selected from a sampling frame.
- A sampling frame is created. This is a list of people in the target population organised into an order – perhaps alphabetical.
-A sampling system is nominated based on the number of people required for the sample.
- If the target population is 25 people and sample of 5 are needed, every 5th person on the list is chosen.
what are the strengths of systematic sampling?
This method is objective. Once the system for selection has been established the researcher has no influence over who is chosen. This is even more true if the start point is randomly selected.
what are the weaknesses of systematic sampling?
-It is difficult and time consuming to conduct. A complete list of the target population may be extremely difficult to obtain. ·
- Selected participants may refuse to take part.
how does stratified sampling work?
The composition of the sample reflects the proportions of people in certain sub-groups (strata) within the target population. · Before stratified sampling can occur, the researcher must identify the different sub-groups within the target population. This could be age or gender for example. · The proportions needed for the sample to be representative are worked out. · The researcher then calculates how many participants are needed from each subgroup to make up the sample. · These participants are selected randomly using a lottery method
what are the strengths of stratified sampling?
It produces a representative sample because it is designed to accurately reflect the composition of the population. This means that generalisation of findings becomes possible
what are the limitations of stratified sampling?
The identified strata cannot reflect all the ways that people are different, so complete representation of the target population is not possible.
· It is difficult and time consuming to conduct. A complete list of the target population may be extremely difficult to obtain.
- Selected participants may refuse to take part.
how does opportunity sampling work?
-Selecting anyone who happens to be willing or available to take part. ·
- The researcher simply takes the chance to ask whoever is around at the time of their study
what are the strengths of opportunity sampling?
It is convenient and much less costly in terms of time and money
what are the limitations of opportunity sampling?
Samples are unrepresentative of the target population as they are drawn from a very specific area, so findings cannot be generalised to the target population. ·
The researcher has complete control over the selection of participants and may, for example, avoid people they do not like the look of. This is researcher bias.
how does volunteer sampling work?
-An advert is produced, and individuals self-select themselves to take part.
· It is also referred to as self-selection.
what are the strengths of volunteer sampling?
Collecting such a sample is easy. It requires minimal input from the researcher, so it is less time consuming. · The researcher ends up with participants who are more engaged than other sampling methods.
what are the limitations of volunteer sampling?
Volunteer bias is a problem. Asking for volunteers may attract a certain profile of person, that is one, who is curious and more likely to try to please the researcher. This reduces the representativeness and thus generalisability of the sample.
