1. A server for communicating with a plurality of monitoring devices via a network, each of the monitoring devices acquiring monitoring variables (1˜H; H is an integral number larger than 1) from an observation target and generating an individual multidimensional distribution of the monitoring variables, the server comprising: a receiving unit configured to collect the individual multidimensional distribution from the each monitoring device, a first space defined by axes of the monitoring variables (1˜H) being divided into a plurality of first elements at the each monitoring device, the individual multidimensional distribution representing a probability density or a frequency of the monitoring variables belonging to each of the first elements in the first space; a first server side generation unit configured to generate first sampling data by sampling the individual multidimensional distribution collected, to determine a first discretion parameter using the first sampling data, the first discretion parameter indicating a method for dividing the first space, to divide the first space into a plurality of second elements by the first discretion parameter, and to generate an overall multidimensional distribution representing a probability density or a frequency of the first sampling data belonging to each of the second elements in the first space; a statistical estimation unit configured to determine indexes (1˜K; K is an integral number larger than 1) to evaluate a state of each observation target from the monitoring variables, using the overall multidimensional distribution; a second server side generation unit configured to generate a second sampling data by sampling the overall multidimensional distribution, to calculate index data of the indexes (1˜K) by calculating the statistical models with the second sampling data, to determine a second discretion parameter using the index data, the second discretion parameter indicating a method for dividing a second space defined by axes of the indexes (1˜K), to divide the second space into a plurality of third elements by the second discretion parameter, and to generate an overall index multidimensional distribution representing a probability density or a frequency of the index data belonging to each of the third elements in the second space; and a transmission unit configured to transmit the overall index multidimensional distribution and the statistical models (1˜K) to each monitoring device.