Adsense undercounting impressions?

[incka]

My page views show about double what adsense says... Is this normal?

[r2d2]

Remember your stats will show spider visits as page views, whereas adsense wont show these.

Also I forget whether PSA ads appear as impressions? Could it be that?

[intelliot]

I think PSAs do appear as impressions.

However, it is fairly normal. As mentioned above, spiders will count as impressions. In addition, some users may not have Javascript turned on, load the page completely, etc.

[Dan Morgan]

I see anything from 40/100 to 80/100 ratios with regard to banner impressions vs banner enabled pages.