The PMI aggregator aggregates and sorts the PMI statistics in intervals. This interval is called the statistics aggregation interval.
You can use wpfAdmin.bat|wpfadmin setStatisticsInterval INTERVAL--id PMI_SUBSCRIPTION_ID to set the partition count for one PMI subscription. You can also use Java code, jacl script, or jython script to get the com.ibm.websphere.wpf.jmx.WPFJMX MBean instance, and change the statistics aggregation interval through the MBean.