What form does statistics usually take
Data matrix, observations on the rows, columns contain variables, cells represent variables, file depends on the format
Measures of central tendency
Mean, mode, median
What is the mean?
Average or arithmetic mean
What is the median?
Observation in the middle when ranked from lowest to highest
What is mode?
Value that occurs most frequently
Useful properties of mean, mode and median
Easy to compute new mean if origin is shifted, Easy to compute when there is a change in scale
What are measures of dispersion
Range, Percentiles, Quartiles, Variance, Standard deviation
What is range?
Largest value - smallest value
What is percentiles?
Divide distributions into the 100ths
What are quartiles?
Divides data into quarters, often represented in a box plot
What is variance?
Deviation from the mean
What is the formula for variance?
Differences of all the numbers from the mean are squared and then added together and then divided by the number of variables (if there is the entire population)
What is standard deviation?
Is used to make variance more useful, so we square root it to get a typical distance of observations from the mean
What are frequencies?
Use of categorical data, which can be seen as relative frequencies, proportion or percentages
What are Proportions?
Number of observations in category divided by total number of observations (what proportions are in what categories)
What are relative frequencies?
Proportions or percentages in different categories and can be represented with a bar graph to show distribution
What are histograms?
Frequency distributions for quantitative variables
