Categorical Variables
A variable that takes values that are labels, placing each item/individual into a GROUP.
Quantitative Variables
A variable that takes number values that are quantities - COUNTS or MEASUREMENTS.
Retrospective Study
An observational study in which observational units are selected a point in time and data are gathered from the past.
Prospective Study
An observational study that selects observational units a point in time and gathers data at that time and into the future.
Population
The entire group of items or individuals that we want information about.
Sample
Subset of items or individuals in the population from which we want to collect data
Explanatory Variable
Variable that many help predict or explain changes in a response variable.
Response Variable
Variable that measures an outcome of a statistical study.
Association
A relationship between two variables in which knowing the value of one variable helps us predict the value of the other.
Marginal Frequency
Gives the percentage or proportion of an observational units in a two-way table calculated by dividing the row or column total by the total for the entire two-way table.
Joint Frequency
Gives the percentage or proportion of units in a two-way table that is calculated by dividing the value in one cell by the total for the entire two-way table.
Relative Frequency
Gives the percentage or proportion of units out of the grand total of items/individuals.
Conditional Frequency
Gives the percentage or proportion of units that have a specific value for one specific value calculated by dividing the value in one cell of a two-way table by the total for the appropriate row or column.
Discrete Variables
A quantitative variable that can take a countable set of possible values with gaps between them on the number line.
Continuous Variable
A quantitative variable that can take any value in an interval on a number line (no gaps)
Skew Left
When a distribution has the majority of the values on the right hand side with a TAIL ON THE LEFT
Skew Right
When a distribution has the majority of the values on the left hand side with a TAIL ON THE RIGHT
Symmetric
When a distribution looks approximately the same on both sides of the distribution
Outlier
A values that is unusually small or large compared to the rest of the data
Mean
Numerical average
Median
The middle value or average of the middle two values
Mode
The value(s) that occurs that most often
Unimodal - One value occurs the most (one peak)
Bimodel - Two values occur the most (two peaks)
Range
Max - min
IQR
Q3 - Q1
Standard Deviation
Measures the typical distance of the values in a distribution from the mean.
Variance
Standard deviation squared
Z score (standardized score)
Tells how many standard deviations from the mean a value falls.
z = (data - mean)/standard deviation