This tool can be used to estimate the Pearson product-moment correlation coefficient (r) for each pair among a group of attributes associated with the database file of a shapefile. The r-value is a measure of the linear association in the variation of the attributes. The coefficient ranges from -1, indicated a perfect negative linear association, to 1, indicated a perfect positive linear association. An r-value of 0 indicates no correlation between the test variables.
Notice that this index is a measure of the linear association; two variables may be strongly related by a non-linear association (e.g. a power function curve) which will lead to an apparent weak association based on the Pearson coefficient. In fact, non-linear associations are very common among spatial variables, e.g. terrain indices such as slope and contributing area. In such cases, it is advisable that the input images are transformed prior to the estimation of the Pearson coefficient, or that an alternative, non-parametric statistic be used, e.g. the Spearman rank correlation coefficient.
The user must specify the name of the vector shapefile and specify which attribute fields to include in the correlation analyses. Correlations will be calculated for each pair of attributes and presented in a correlation matrix text output.
The following is an example of a Python script that uses this tool:
wd = pluginHost.getWorkingDirectory()
# Input data has the shapefile name followed
# by each attribute included in the analysis,
# separated by semicolons.
inputData = wd + "neighbourhoods.shp" + ";" + "NUM_SCHOOLS" + ";" + "INCOME" + ";" + "POP_DENSITY"
args = [inputData]
pluginHost.runPlugin("CorrelationForAttributes", args, False)
This is a Groovy script also using this tool:
def wd = pluginHost.getWorkingDirectory()
// Input data has the shapefile name followed
// by each attribute included in the analysis,
// separated by semicolons.
def inputData = wd + "neighbourhoods.shp" + ";" + "NUM_SCHOOLS" + ";" + "INCOME" + ";" + "POP_DENSITY"
String[] args = [inputData]
pluginHost.runPlugin("CorrelationForAttributes", args, False)