A performance diagnostic server acquires time series data that indicates the number of executions per time from a multi-tier system and calculates, on the basis of the time series data, a correlation coefficient of processing types that are executed by a server in each tier. The performance diagnostic server calculates, from a correlation coefficient of processing types, a partial correlation coefficient by removing the effect of the trend of the entire multi tiers and updates the correlation coefficient of the processing types on the basis of the calculated partial correlation coefficient.