AS Statistics Flashcards
Population
The whole set of items that are of interest
Sample
Subset of the population intended to represent the population
Sampling Unit
Each individual thing in the population that can be sampled
Sampling Frame
Sampling units of a population are individually named or numbered to form a list
Census
Data collected from the entire population
Advantages of a Census
- should give a completely accurate result
Measures of Central Tendancy
Values to do with the centre of data e.g. mean, median and mode
Comparing Box Plots
- IQR + context
- Median + context (“on average”)
Comparing Data
- a measure of location
- a measure of spread
Bivariate Data
Data which has pairs of values for two variables
Casual Relationship
Two variables have a casual relationship if a change in one variable causes a change in the other
Interpolation
Making a prediction based on a value inside the range of given data
Extrapolation
Making a prediction based on a value outside the range of given data
Systematic Sampling
Required elements are chosen at regular intervals in an ordered list
Stratified Sampling
Population divided into groups (strata) and a simple random sample carried out in each group
Quota Sampling
Divide population into groups then determine the size of each group in the sample to reflect proportions within the population. Actively choose people within each group until the quota of each group is filled
Opportunity Sampling
Find people at the same time the survey is being carried out
Random Sampling
Each thing in the sampling frame has an equal chance of being chosen, in order to avoid bias
Advantages of a Census (1)
- should give a completely accurate result
Disadvantages of a Census (4)
- time consuming
- expensive
- large volume of data to process
- can’t be used when testing involves destruction
Advantages of a Sample (3)
- quicker
- cheaper
- less data to process
Disadvantages of a Sample (2)
- may not be representative
- possible bias
Advantages of Random Sampling (2)
- bias free
- easy and cheap to implement
Disadvantages of Random Sampling (3)
- not suitable when population size is large
- sampling frame needed
- may not be representative
Advantages of Systematic Sampling (3)
- simple and quick to use
- suitable for large samples/populations
- no bias
Disadvantages of Systematic Sampling (2)
- sampling frame needed
- bias can be introduced if sampling frame not random
Advantages of Stratified Sampling (2)
- reflects population structure
- guarantees proportional representation of groups within population
Disadvantages of Stratified Sampling (2)
- population must be clearly classified into distinct strata
- selection within each stratum suffers from same disadvantages as random sampling
Advantages of Quota Sampling (4)
- allows small sample to be representative
- no sampling frame needed
- quick, easy and inexpensive
- allows for easy comparison between different groups
Disadvantages of Quota Sampling (2)
- can introduce bias
- population must be divided into groups
Advantages of Opportunity Sampling (2)
- easy to carry out
- inexpensive
Disadvantages of Opportunity Sampling (2)
- unlikely to provide a representative sample
- highly dependent on individual researcher
