Correlations are special types of Connection functions since they do not result in the creation of new raster layer. Instead the correlation information is stored within a seperate file.The correlation output can be viewed through drag and drop of the connection within the file tree into the right window.
If all files contain a NODATA value for the same pixels they are excluded from calculation. If only one file has a NODATA value, the treatment can be specified. There are three options
Both, Pearson and Spearman Rank Correlation offer the poosibility to calculate partial correlation coefficients and p-values calculated from a student-t-distribution.
The connection function pearson product moment correlation coefficient is a measure for the linear correlation between two variables x and y with a value between +1 and -1. While + 1 indicates a perfect positive correlation -1 indicates a perfect negative correlation. In both cases all data points are on exactly on one line in a xy diagram. The pearson correlation coefficient is calculated according to the formula
The connection function spearman rank correlation coefficient is a measure of the correlation (not necessarily linear) between two variables x and y with a value between +1 and -1. While + 1 indicates a perfect positive correlation -1 indicates a perfect negative correlation. It is the pearson correlation coefficient between the variables x and y after they have been converted to ranks. NODATA values are pairwise deleted from calculations.
The formula for the calculation of the correlation coefficient is