18.1 - Populations and Samples Flashcards
What is the definition of a simple random sample?
A type of procedure where every possible sample (of a given size) has an equal chance of being selected
Is a simple random sample biased?
No
What is an example of a simple random sample?
A random number generator (such as the randint function on a calculator)
What is the common practice with replacing values?
It is not done
Why?
Because it means that no piece of data could be selected more than once
Why are simple random samples hard to execute in process?
Because very large data sets are generally chosen, and this means that getting a list of the entire population is a challenge, so the sampling procedure cannot be applied fully
What is opportunity sampling?
Sampling based on availability and/or convenience
Is an opportunity sample biased?
Yes
What are the benefits of an opportunity sample?
Cheap and convenient
What is systematic sampling?
Taking data values at regular intervals in the population, with the starting point chosen at random
What is key about the list of data for systematic sampling?
It must be ordered in some way (e.g. alphabetically)
Why is this key for systematic sampling?
Because it means that a good spread of data is collected, thus ensuring that the sampling method is random
Why is systematic sampling less random than simple random sampling?
Because it is no longer independent
What is the other drawback of systematic sampling?
It requires a list of the entire population
What are the benefits of systematic sampling?
Avoids unwanted clustering of data and practically easier than a random number generator
What is stratified sampling?
Splitting the population into groups based on factors relevant to the research, the random sampling from each group, in proportion to the size of that group
What does this produce?
A representative sample over the factors identified
What is the drawback, and what does this mean, of stratified sampling?
Needs an entire list of the population and additional information about each member, which is time-consuming and expensive
What is the common alternative to stratified sampling?
Quota sampling
What is quota sampling?
Splitting the population into groups based on factors relevant to the research, then opportunity sampling from each group until a required number of participants are found
Is quota sampling biased?
Yes
What is the benefit of using quota sampling?
It produces a representative sample over the factors identified
What is cluster sampling?
Splitting the population into clusters based on convenience, then randomly choosing some clusters to study further
What type of sample does cluster sampling produce?
An unrepresentative one
