# Definitions

### Questions and Data

Data
An item of (chiefly numerical) information, especially one obtained by scientific work, a number of which are typically collected together for reference, analysis, or calculation. From Latin datum: that which is given. Facts.
Variable
A characteristic of an object or observational unit that can be measured and recorded.
Numerical Variable
A variable that take numbers as values and where the magnitude of the number has a quantitative meaning.
Categorical Variable
A variable that take categories as values. Each unique category is called a level.
Continuous Numerical Variable
A numerical variable that takes values on an interval of the real number line.
Discrete Numerical Variable
A numerical variable that takes values that have jumps between them.
Ordinal Categorical Variable
A categorical variable with levels that have a natural ordering.
Nominal Categorical Variable
A categorical variable with levels with no ordering.
Data Frame
An array that associates the observations (downs the rows) with the variables measured on each observation (across the columns). Each cell stores a value observed for a variable on an observation.
Unit of Observation
The class of object on which the variables are observed.
Summary
A numerical, graphical, or verbal description of an aspect of data that is on hand.
Generalization
A numerical, graphical, or verbal description of a broader set of units than those on which data was been recorded.
Causal Claim
A claim that changing the value of one variable will influence the value of another variable.
Prediction
A guess about the value of an unknown variable, based on other known variables.