MR Y12 - Statistics Flashcards
Population
The whole set of items that are of interest e.g population of a town
Raw data
Unprocessed data
Census
A procedure observing or measuring every member of a population
Sample
A selection of observations from a subset of a population used to find information about the population as a whole
Advantages and disadvantages of a census
Advantages:
- Should give a completely accurate result
Disadvantages:
- Time consuming and expensive
- Hard to process the large quantity of data
Advantages and disadvantages of a sample
Advantages:
- Less time consuming and expensive than a census
- Fewer people are required to respond
- Less data to process than a census
Disadvantages:
- Data may not be accurate
- Sample may not be large enough to provide information about small sub-sections of the population
Sampling units
Individual units of a population
Random sampling
Non-biased selection where every member of the population has an equal chance of being selected
Simple random sampling
Where every sample has an equal chance of being selected e.g picking names out of a hat
Systematic sampling
Where elements are chosen at regular intervals from an ordered list
Stratified sampling
Where the population is divided into mutually exclusive strata and a random sample is taken from each
Advantages and disadvantages of simple random sampling
Advantages:
- Free of bias
- Easy and cheap to implement for small sample sizes
Disadvantages:
- A sample frame is needed
- Not suitable for large population sizes due to being time consuming and expensive
Two types of non-random sampling
Quota sampling
Opportunity sampling
Three types of random sampling
Simple random sampling
Systematic sampling
Stratified sampling
Quota sampling
Where a sample is selected to reflect the characteristics of the whole population
Opportunity sampling
Where the sample is taken from people who are available at the time the study is carried out who fit the criteria
Advantages and disadvantages quota sampling
Advantages:
- Allows a small sample to be representative of the population
- Allows easy comparison between different groups in the population
Disadvantages:
- Non-random sampling can introduce bias
- Population must be divided into groups which may be expensive or inaccurate
Advantages and disadvantages of opportunity sampling
Advantages:
- Easy to carry out
- Inexpensive
Disadvantage:
- Unlikely to be representative
- Highly dependent on the researcher
Quantitative data / variables
Data / variables associated with numerical observations
Qualitative data / variables
Data / variables which are associated with non-numerical observations
Continuous variable
A variable that can take any value in a given range
Discrete variable
A variable which can only take specific values in a given range
Class boundaries
Maximum and minimum values that belong in each class
Midpoint
Average of the class boundaries
Class width
Difference between the upper and lower class boundaries
Sampling frame
When units of a population are given individual names / numbers to form a list called a sampling frame
