The correlation coefficient is a measure of the interrelationship between variables, the correlation. Interrelationships can be directly related, namely when one variable influences a second variable in the same direction. This is the case, for example, with a phototransistor when the voltage increases with the incidence of light. This is a positive correlation, which is expressed in a positive correlation coefficient. If there is no correlation between the two variables, the correlation coefficient becomes zero, and if the correlation is in the opposite direction, for example if the resistance value of a thermistor
falls as the temperature rises, the correlation and the correlation coefficientare negative.
The correlation coefficient can only be used for linear correlations and can take positive and negative values.
The value range itself is between -1, 0, +1. For the closest correlation, the value can be +1 or -1, depending on whether the immediate correlations are of the same or opposite sense.