I have tested it again by picking the top 50 percent of the records.
PARAMETERS [Forms]![frmReport]![startdate] DateTime, [Forms]![frmReport]![enddate] DateTime;
SELECT TOP 50 PERCENT qryEpisode.Patient_Name, qryEpisode.EpisodeID, qryEpisode.ReferralToTreatment
FROM qryEpisode
WHERE...