Is your impression count accurate?

Mine is not

[mallu]

My impression count is around 25% less than what webalizer reports.

Yours?

[Jenstar]

Here is what the AdSense FAQ says about differing impression counts:

We count impressions only when our ad code is executed by a user's browser. There are therefore several factors that would cause a discrepancy between the impressions you register and the impressions listed in your AdSense account. Instances that wouldn't execute the code include:

Other spiders, robots, crawlers from other search engines
Browsers that don't have JavaScript enabled or don't support JavaScript
Browsers that don't support the <iframe> tag
Programs that people may have written to grab website content

[Mauricio]

Don't forget the PSA and the simple and plain Adsense failure.

Mine are too 25% under server stats but some days is worse, some days is better.

[crookyboy]

me too, sometimes my impressions fall by half even though my site has had no drop in page views. You should be more concerned about your clicks dropping.

[aroach]

Mine seems to be higher than what my web stats package says. I always suspected my stats were not accurate.

[universetoday]

I'm about 25% under as well. That's close enough for me.

[richmondsteve]

To build on what Jenstar said, also note that in the AdSense reporting the day begins at midnight PST (GMT-8). If your web server's logs (or reports) use a different timezone the stats won't match.

Also, though at least one person here has sworn that the public service ads (unpaid ads) do not count towards the impressions in the AdSense reporting (and I suspected that was the case previously), my own current tests show otherwise. On one site I've limited the AdSense code to a single page the last few days and the page has shown nothing but unpaid ads yet shows ~1,000 daily impressions which nearly matches the page views according to the web server's logs.

[Rearden]

Webalizer's stats are a bit optimistic, since it includes visits from spiders and the like. I prefer awstats, myself.

[Jenstar]

On one site I've limited the AdSense code to a single page the last few days and the page has shown nothing but unpaid ads yet shows ~1,000 daily impressions which nearly matches the page views according to the web server's logs.

That is good to know, richmondsteve. I think many just assumed that PSAs would not count towards the impressions.