joined:Apr 1, 2016
How does Adsense determine what the fill rate should be to maintain 100% earnings?
They do not disclose how they determine the values of the ad-balance feature. I find this somewhat frustrating. But as far as I can tell it is based on the distribution of ads that appeared on you site over relatively short time period (day or two). Look at the "revenue profile" report in Adsense. What the system does is takes that curve and chops off the left side. How far left depends on the setting.
How accurate will this be for sites with relatively low traffic?
Accuracy has more to do with the slope of the revenue profile curve, a flat curve will generate some wild results because little shifts up or down can move the target (left, right position) by big margins. Say the change in the slope between 90% and 25% is ($0.07 @50%. - $0.05 @90%) = $0.02. Now say you set the ad balance at %50, meaning you forgo any ads that will pay you less than $0.07 (on average, it is set to % not $ value). Then suddenly the market changes slightly and moves up by a penny so %50 is at 0.08. But the slope stays the same, now you are suddenly forgoing 20% more ads that initially anticipated. Since now 70% of your ads are earning $0.07 or more, but you are only showing 50% of them due to your initial setting.
I don't know if this clear but the basic idea is:
If you have a flat curve over most of the range then the ad-balance is probably not a good tool for you site. The ad-balance tool really works well when you have a nicely sloped line that flattens at the left end. In this case, the ad-balancer is preventing what essentially is your un-sellable ad space to be removed from the market. Conversely, if there is no market at all for you ad space (the whole of your curve is flat), then the tool will basically block everything. In which case you may want to look at your website targeting, in attempt to find some interested advertisers.
My account is showing 100% rev at 30% fill.
See my comment above
What is the time period adsense looks back on to gauge this balance.
Not clear, as far as I can tell it is a few days at most.
I have noticed my cpc increased quite dramatically in the last few days when I set the fill rate at a pretty low level, but that could also be because my site is coming out of a sustained period in which adsense performed poorly (based on historic performance). So I am not sure what to attribute this to.
It is expected that your CPC increases dramatically, The CPC is the average CPC over time period selected by you in the report. If you remove all the ad clicks that paid you only a penny or two, then one naturally expect the average to go up. Example: before you had 10 click per day, 9 x $0.03, 1 x $0.73 == avg CPC of $0.10. If the you block impression and clicks for ads paying less than $0.05 per click, you are left with 1 click at $0.73, so your CPC for the same period is now $0.73. But you only earned $0.73 instead of $1.00. This does not mean that you are earning more money, it is only a side effect of the reporting. Similarly CTR and RPM should also go up, because you have fewer impressions, again this an expected reporting side-effect and will have not impact on your earnings. IMO what you observed has little to do with poor past performance.
With all that being said, the biggest benefit for me, has been the ability of ad-balance to have noticeable positive impact on eliminating spammy ads. I do not have any hard evidence or proof, because so many other things have been changing over the same period that I have been using the ad-balance, but I feel that the elimination of the spam ads has provided a better experience for my users that allows them to see only quality ads, this in turn must have a positive impact on earnings.