Have a look at the purge accumulator tool, this synchronizes the data in the stats database with the data in the main database and then deletes the statistical data from the main database that is more than 180 days old
The default is to purge stats data that is older than 180 day, but you can change that value in the bb-tasks.xml file (found in Blackboard config directory)
Find this entry:
<!-- Data integration log entry cleanup. Must run on at least one application server -->
<task-entry key="bb.data.integration.purge" version="60">
<task classname="blackboard.platform.dataintegration.DataIntegrationLogCleanupTask">
<property name="delay" value="60000" />
<!-- Daily -->
<property name="period" value="86400000" />
</task>
</task-entry>
And then change the value of "period", based on how many milliseconds between task invocations that you wish to keep the stats data for
More info here:
http://kb.blackboard.com/display/KB/The%20PurgeAccumulator%20task?sso=587EFCA621F8A70481389864B5C587660ACE0A4393381C4AA57B35851DA8BDAA8FCE1CAEE59913EBCF0C8D8FF43805D4
