The PPM sample is much LOWER than the diary sample in SF...about a third as many. Somewhere around 2240 meters, and there were three times as many books. One thing that radically affects PPM compared to diaries is that a PPM panelist can be on the panel for a year and a half, so if you happen to get a panel that has lots of partisans for a particular station, they look great over that period (as long as the panelists carry the meter...but if they slack off, ARB kicks them off after a couple warnings.)