What is random sampling?
- When every member of a population has an equal chance of being selected
- Fair and unbiased
Describe one way in which we might conduct a random sample.
- List all members of the population and assign a number from x to y
- Use a random number generator or calculator to randomly generate z numbers
- Select all items with corresponding numbers and ignore repeats.
- On calculator: RanInt#(x,y)
What are some methods of non-random sampling? (7)
- Judgement sampling
- Quota sampling
- Opportunity sampling
- Cluster sampling
- Systematic sampling
- Stratified sampling
- Capture-Recapture
What is judgement sampling?
Using your judgement to select a sample that represents the population
What is quota sampling?
Grouping the population by shared characteristics and interview a “quote” from each group e.g. 10 males over 25
What is opportunity sampling?
Using items that are available at the time
What is cluster sampling?
When the data naturally splits into clusters then using random sampling to select items
What is systematic sampling?
Choosing a random starting point from the sampling frame and then choosing items at regular intervals
What is stratified sampling?
- Dividing the population into strata based on shared characteristics and then taking a random sample from each stratum that is proportional to its size in the population
- Formula: sample size x (stratum size/total population)
What does the capture-recapture formula assume?
- Population hasn’t changed
- Probability of capture is equal for all members
- Marks haven’t been lost
- Sample is large enough to represent the population
