Sampling Flashcards
What is a Population?
The Population is the set of things that you are interested in. For example all people in the UK
What is a Census?
A Census observes or measures every member of the population
What is a Parameter?
A Parameter is a number that describes the entire population such as the mean
or standard deviation of the population
What is a Sample?
A Sample is a subset of a population. A sample is used to find out information
about the population as a whole
What is a Statistic?
A Statistic is a value calculated from a sample such as the mean or standard deviation of the sample. A statistic can be used to estimate a parameter. e.g. the mean of a given sample is an estimate of the mean of the population
What is a Sampling Unit?
A Sampling Unit is an individual unit from the population. For example, a particular person living in the UK
What is a Sampling Frame?
A Sampling Frame is a list of all the sampling units in the population. The electoral register is an example of a sampling frame for the population of the UK.
What are the advantages and disadvantages of taking a sample over a census?
Advantages:
- Less time consuming, less expensive and less data to process
Disadvantages:
- May be inaccurate, the sample may not be large enough to represent small subgroups of the population
What are the advantages and disadvantages of taking a census over a sample?
Advantages:
- It should give a completely accurate result
Disadvantages:
- Time consuming, expensive, large amounts of data to process and can not be used when the testing process is destructive.
How do you take a Simple Random Sample?
1 – Number all items in the population
2 – Use random numbers to select a sample (ignore repeated numbers)
How do you take a Systematic Sample?
1 – Number all items in the population
2 – let n = population size/sample size
3 – Use random numbers to select a number one to n. This is the first item
4 – choose every nth item after that
How do you take a stratified sample?
1 – Divide the population into groups
2 – Work out how many to sample per group using (number in group/number in population) x sample size
3 – Use simple random sampling to select items from each group
When should you use a random sample? And what should you use if a random sample is impractical?
When you have a sampling frame. Otherwise use a non random sampling method
How do you take an Opportunity sample?
Choose the first items available to you until you have measured the required number of items (ignore repeat entries and excess data)
How do you carry out Quota sampling?
1 – Divide the population into groups
2 – Work out how many to sample per group using (number in group/number in population) x sample size
3 – Carry out Opportunity sampling until each quota is met (ignore repeat entries and excess data)
