Correlations come in three flavors.
- Positive correlation. Example: temperature with ice cream sales. As temperature goes up, on average ice cream sales go up.
- Negative correlation. Example: hours spent watching TV with grades in class. The more hours a student spends watching TV per week, typically the lower his/her Grade Point Average (GPA).
- Zero correlation. Example: number of letters in the name of a city with longitude. Cities with long names are just as likely to be located North as South.