Many people have noticed that version 2.4 of OpenX handles banner and campaign weight differently from version 2.0. Let’s work with a simple but real life example: There are two advertisers. Each advertiser has one campaign, but the second advertiser happens to have provided two banners that need to be rotated.
In version 2.0 each campaign would have received 50% and then the two banners of the second campaign would each split that 50% to get 25% of the probability.
But in OpenX 2.4 things are a little different. The picture below illustrates this: the campaign with two banners grabs 66,66% of the total probability, and the campaign with one banner gets the remaining 33,33%.
There is a way to get around this, and it requires only a little change in the way campaigns are defined. It all has to do with campaign weight. To continue with the example above, the campaign that has 2 banners must be given a lower weight to reflect there are more banners in it. Most people use the default weight that OpenX assigns to a campaign, but you can change that manually.
Here’s the recipe: give each campaign a weight of 100 to start with, but then adjust the campaign weight when you add more banners to it. If it’s a campaign with two banners, change the campaign weight to 50, or if the campaign has 4 banners, change the campaign weight to 25. Then when you go back to the probability screen the two campaigns are linked to, you’ll notice that the probabilities there have also changed, as can be seen in this image.
(This tip applies to OpenX 2.4.x and was initially written on June 25, 2008)