correlation

A relationship between two variables.

A correlation has a value between -1 and 1, and is an estimate of how closely two variables covary. A negative score suggests a negative correlation ("as one goes up, the other goes down"), while a positive score suggests a positive correlation ("as one goes up, the other goes up"). A value close to 1 or -1 is a strong correlation, while a value of zero means that there is no correlation at all. An example of a positive correlation is cost of a TV and width of a TV. Higher cost tends to equal greater width, as a general trend. An example of a negative correlation is age and health. Instances that go against the trend of the correlation (such as a very old, very healthy person) are called outliers. A useful way of visually showing a correlation is a scatterplot.