Sampling Methods Flashcards
what is a target population
This is the overall group the experimenter wants to study.
what is a sample?
A group of people who take part in a research investigation. The sample is drawn from a (target) population. The more representative of the target population, the more the researcher can generalise.
What is Random sampling?
Compile a list of all members in the target population, every name assign a number, sample generated via: a lottery system e.g. names in a hat, computer based generator.
Everyone has an equal chance of being selected
strengths of random sampling
- everyone has equal chance of being selected.
- If done can eliminate researcher bias and should be good representation of target population.
disadvantages of random sampling
- very difficult to achieve in reality
- Timely and costly as a complete list of the target population may be difficult to obtain.
describe systematic sampling
Choose subjects in a very systematic way. A sampling frame is produced, which is a list of people in the target population organised into, for example alphabetical order. Then, every ‘nth’ (e.g. 3rd, 5th) participant on the list of names from the sampling frame.
strength of systematic sampling
Avoids researcher bias
weakness of systematic sampling
Periodic traits- there could be an hidden trait in the population.
eg sample would be unrepresentative or you have all females being selected from a class list
describe stratified sampling
- Select people to represent target population exactly.
- Dividing the target population into important strata (subcategories)
- Selecting members in proportion that they occur in the population
E.G. 2.5% of British are of Indian origin, so 2.5% of your sample should be of Indian origin - To meet required number, participants are selected by random sampling.
strength of stratified sampling
- Avoids researcher bias
- Does provide an excellent representation of population and can generalise from results.
weaknesses of stratified sampling
- Very expensive and time consuming.
- Is not perfect, as the identified strata cannot reflect all the possible ways people are different.
what is opportunity sampling
This is when you use a sample that is available to you and willing to participate e.g. market researchers.
strength of opportunity sampling
Very easy and quick, therefore convenient.
weakness of opportunity sampling
- Very difficult to obtain true representation of target population so the sample may be unrepresentative.
- Researcher bias, as the researcher has control over who is being selected
what is volunteer sampling
Self-selection- involves participants selecting themselves to be part of the sample
strengths of volunteer sampling
Very easy and quick compared to other research methods, as the p’s come to you, therefore convenient.
weakness of volunteer sampling
Volunteer bias, as it may attract a certain type of person, i.e. those that are helpful, so the sample may be unrepresentative.
