Correlation coefficient
Topic: Geographical Data: Sources, Compilation and Processing · NCERT: Class 12, Ch 4 "Spatial Information Technology"
Meaning
A correlation coefficient is a single number between −1 and +1. It shows how closely two variables (things that change from place to place or over time) move together, and in which direction. A positive value means both rise together. A negative value means one falls as the other rises. A value near zero means there is little or no link. The closer the number is to −1 or +1, the stronger the link. Karl Pearson's r is used for measured values. Spearman's rank correlation is used when places are only ranked.
Example
As you climb from the plains of Haryana up to Shimla in Himachal Pradesh, the temperature drops. So altitude and temperature have a negative correlation. Rainfall and the area under paddy usually have a positive one: wetter districts tend to grow more rice.
Don't confuse with
- Causation (one thing making another happen): a strong correlation does not prove that one variable causes the other. Both may be driven by a third factor.
- Standard deviation: it measures how spread out one variable is. Correlation links two variables.
Related concepts
- Measures of dispersion
- Range
- Mean deviation
- Standard deviation
- Coefficient of variation
- Measures of relationship