How do I handle the exposed pad on the underside of the QFN-32 (RSM) package of the ADS1291/1292?

The datasheet for the ADS1291/1292 doesn't talk about how to handle the exposed pad of the QFN-32 package.  It doesn't say if it's ground or not, nor whether to connect it to ground or not, as is often done.  What's the correct thing to do?

Thanks,
Scott