Descriptive Statistics
Four different scales for presenting info.
Nominal: Give something a name
ex: 1: Male, 2: Female
Ordinal: Put in order, but not equal distance
between steps ex: ranking of state
population
Interval: Ordinal, but equal steps
ex: days of the week
Ratio: Interval, but has an absolute zero
ex: inches
Central Tendency
Mode: most frequent score
can have multiple modes, use in nominal
data
Median: middle score
use when there are uncommon extremes
ex: salary
Mean: average score
be careful when using
ex: Aggies crossed the river that averages 2
ft. deep and drowned
Measures of Dispersion
Range (highest score – lowest score)
Semi-interquartile range: (Q3-Q1)/2
(75%-25%)/2
Standard Deviation: how much the scores
deviate from the mean
Calculate Standard Deviation
Set of numbers
Find the mean
(x-mean)2
Find the sum of all numbers,
divide by number of original
units, then find the square root
Source: Wikipedia.com