adsense: how do you juggle between ad units and link units?

[rowan]

I have a site that's making a small amount of adsense income (about 25k impressions per day). I am experimenting with both ad and link units, so I've set up a system that lets me define the ratio between the two (eg 30% of impressions to link units, 70% to ad units). The problem is that the "winning" eCPM (the unit with the maximum eCPM) keeps flipping back and forth, and it's not always by a small amount either. For example:

yesterday:
linkunit 7815 impressions $0.37 eCPM
adunit 17853 impressions $0.85 eCPM

ok, right choice there, but so far today link units are making a better eCPM...

linkunit 1869 impressions $1.02 eCPM
adunit 15259 impressions $0.84 eCPM

If you use both link and ad units, do you have a system to decide between the two?

[SmokeyTheBear]

longer testing ? thats about all i do

[rowan]

Originally Posted by SmokeyTheBear

longer testing ? thats about all i do

What if the long term trends are not consistent with short term? You're missing out on $.

It's a pity G don't have a stats API to automate it and squeeze out the maximum benefit... I guess I could do something manually like:

if (stats file manually updated less than 24 hours ago) {
  total = adunit eCPM + adlink eCPM
  number = random(total)
  if (number <= adunit eCPM) {
    displaytype = adunit
  } else {
    displaytype = adlink
  }
}