Correlation. When two sets of data are strongly linked together we say they have a High Correlation.

The word Correlation is made of Co- (meaning "together"), and Relation Correlation is Positive when the values increase together, and Correlation is Negative when one value decreases as the other increases Like this: Correlation can have a value: Normal Distribution. Data can be "distributed" (spread out) in different ways.

But there are many cases where the data tends to be around a central value with no bias left or right, and it gets close to a "Normal Distribution" like this: A Normal Distribution. Standard Deviation and Variance. Deviation just means how far from the normal Standard Deviation The Standard Deviation is a measure of how spread out numbers are.

Its symbol is σ (the greek letter sigma) Quartiles. Quartiles are the values that divide a list of numbers into quarters.

First put the list of numbers in order Then cut the list into four equal parts The Quartiles are at the "cuts" Like this: Example: 5, 8, 4, 4, 6, 3, 8 Put them in order: 3, 4, 4, 5, 6, 8, 8 Cut the list into quarters: Calculating the mean from a frequency table. It is easy to calculate the Mean: Add up all the numbers, then divide by how many numbers there are.

Example 1: What is the Mean of these numbers? Standard Deviation Formulas. Deviation just means how far from the normal Standard Deviation The Standard Deviation is a measure of how spread out numbers are.