positive correlation

A positive correlation is a relationship between two variables such that their values increase or decrease together. 

Correlation is expressed on a range from +1 to -1, known as the correlation coefficent. In a perfect positive correlation, expressed as +1, an increase or decrease in one variable always predicts the same directional change for the second variable. If two variables sometimes but not always change in tandem, the correlation is expressed as greater than zero but less than +1. Values below zero express negative correlation: As the value of one variable increases, the other decreases. Zero indicates a lack of correlation: There is no tendency for the variables to fluctuate in tandem either positively or negatively.

Examples of positively correlated variables include:

• Hours spent studying and grade point averages.
• Education and income levels.
• Poverty and crime levels.
• Evaluated stress levels and blood pressure readings.
• Smoking and lung disease.

There’s a common tendency to think that correlation between variables means that one causes or influences the change in the other one. However, correlation does not imply causation. There may be an unknown factor that influences both variables similarly.