Statistics Flashcards
What is a census?
Measures every member of a population
What is a sample?
Observations taken from a subset of a population to get information about the whole.
Advantages of census
Completely accurate
Disadvantages of census
Time and money consuming, impossible if process involves destroying the subject, hard to process loads of data
Advantages sample
Less data, less time and money consuming, less subjects needed.
Disadvantages sample
May not be accurate, not large enough
Simple random sampling
Assign number to each unit then randomly pick
Systematic sampling
Chosen at regular intervals through a list with the position of where you start random
Stratified sampling
Proportionally picked from each group
Advantages of simple random sampling
No bias, easy/cheap
Disadvantages of random sampling
Not suitable for large groups, sampling frame required
Systematic sampling advantages
Simple, quick, good for large groups
Systematic sampling disadvantages
Sampling frame needed, can introduce bias if frame is not random
Stratified sampling advantages
Accurately represents population structure, guarantees that proportional representation
Stratified sampling disadvantages
Must be pre-classified into strata, selection has same issues as simple random sampling.
Quota sampling
Sampler selects which group the person is put in and ignores when quota is full
Opportunity sampling
Take a sample if the unit suits criteria and is available
Quota sampling advantages
Small sample still representative, no frame
Quota sampling disadvantages
Can be biased, division into groups may be inaccurate and costly
Opportunity sample advantages
Easy, cheap
Opportunity sampling disadvantages
Dependent on sampler and unlikely to give representative sample
Measure of location
Value that describes a position in a data set
Measure of central tendency
Single value describing the centre of the data (mean, median, mode)
When working out lower and upper quartiles how do you round?
UP
Histograms
Frequency density = frequency/class width
Bivariate data
Pairs of values for two variables (one independent and one dependent variable)
What is the least squares regression line?
Line of best fit
Discrete uniform distribution
The probability of each outcome is the same (e.g. a fair die)
Conditions for binomial distribution
Fixed number of trials, two possible outcomes, fixed probability, independent
How to measure outliers?
1.5 x IQR below/above LQ/UQ
How to check whether two events are independent?
P(A and B) = P(A) × P(B) if independent
