To begin with, you can not stop interest based ads from appearing on your site(s).

What happens when you turn off Interest Based Ads.
You supposedly stop Google from using data collected from your site to decided which interest based ads to show your visitors on the site(s) they visit in some unspecified time period after they visit your site.

I guess wasn't very clear about my question. I'd like to get anyone's experience or input on which setting, "on" or "off", is a better choice from the standpoint of CTR and eCPM.

"on" or "off",

CTR or ecpm?

Yup, that is the point....

it doesn't make any difference which setting you use.

If you choose "off" it only affectes the ads on other sites your visitors go to.

So, just to put a fine point on this, your experience is that changing this setting absolutely does not increase or decrease your CTR or eCPM? I see folks mentioning that they've turned off interest based ads when they've become panicked over a slump in these numbers, and I've wondered why.

your experience

The way G has set this thing up, there is NO WAY to compare the effects of on or off, because you can't make the ads not show on your site(s).

I see folks mentioning that they've turned off interest based ads when they've become panicked over a slump in these numbers, and I've wondered why.

Probably because Google, as usual, sends a mixed message on this. On one hand they give us a place to "turn off" interest based ads, and on the other hand they then tell us that turning the ads off won't affect the ads that are shown on our site(s), that they will still show our visitors IBAs, a lot of publishers seem to miss that last part.

But it's that last part that is the problem and why Interest Based Ads (IBAs) might lead to a lower CTR or eCPM.

Your CTR and eCPM from IBAs is going to be at least partly based on what site the ads are based on. If your visitor comes from a site with content that attracts low value ads, then low value ads are probably what are going to be shown on your site,

That's IF IBAs are shown at all, if they have to compete with ads based on the content/context of your site, then they may not even be shown. Right now I don't recall if IBAs have to compete or not.

This interest based ads thing doesn't make sense to me at all. I realize that Google can collect a LOT of information about someone, but unless they can peer into the area where your computer is located, they have no way of knowing if the interest based ads they're showing NOW--which are based on sites visited EARLIER--are of interest to the person using the computer RIGHT NOW.

Computers with multiple users is one reason. The 15 year old son might be searching for model airplanes one minute, and the next the Mom of the household might be looking to buy a birthday gift for her sister, and wondering why she's seeing so many ads for models.

Then, once Mom buys the gift for her sister, the Dad is next on the computer a few hours later, and instead of seeing targeted ads on his favorite car site, he's seeing ads for model airplanes or purses.

How does this relate to better targeted ads? And how long does Google retain this information? After all, once something is purchased, chances are showing ads about it for the next few days will be ignored, since the purchase has already been made, and the user has moved on to other things.

I might be missing a piece of the puzzle, but I can't see how Google can determine that what was interesting to the user 5 minutes ago is still interesting to the current user. Which tells me the ads being shown aren't relevant at all in many instances, and that would certainly explain lower CTRs that so many are reporting.

Dad doesn't care about purses, and won't be clicking on any ads about them.

Well, I agree with all that. I've observed the phenomenon in my own searching. I may have done a search for widgets, but now I'm keen on bodgets, but I see AS believes I'm still obsessed with widgets, even though I've grown sick of them, and won't be clicking on any widget ads.

So, I suppose, in that sense, interest based ads can have a negative effect on our AS revenues but there's no way to compute it. And, I'm assuming that, whether or not interest based ads are turned on or off, has no bearing on what I'm earning in AS revenues at any given time.

I see folks mentioning that they've turned off interest based ads when they've become panicked over a slump in these numbers, and I've wondered why.

"Why" might be a good question. Interest based ads, or lack thereof, might have nothing to do with their slump in numbers.


FarmBoy

I'd like to get anyone's experience or input on which setting, "on" or "off", is a better choice from the standpoint of CTR and eCPM.

My experience was bad, won't try that again. You ask about ctr and ecpm and some folks mention better targeted ads. I can only talk about my experience: I turned that thing on for 15 days and didn't like it. I never had such bad numbers in all my years with Adsense (not even the worst season compares to those 15 days).

I won't consider the kind of ads people were seing... It doesn't matter to me. I gave it 15 days considering 5 days wasn't enough. I remember one or two post here at WebmasterWorld mentioning it was working fine for them but most of the posts I can remember complain about the results.

Just my two cents.

I cannot see any reasonable way I could tell whether interest based ads are doing me any good or not. It's not something I can control, and it's not something I can measure. So I don't mess with it or worry about it.