Determine how many impressions to book
The number of impressions you can book depends on how willing you are to displace or preempt existing inventory.
First, run a forecast for the prospective line item. Remember that your line item's trafficking criteria can greatly affect the number of available impressions.
How forecasting accounts for trafficking criteria
Forecasting takes most trafficking criteria into account when determining available inventory, but there are some details you should keep in mind:Frequency capping
Frequency capping is considered. Because DoubleClick for Publishers uses a 28-day sample, monthly or lifetime frequency caps are not captured as part of the sample data. Consequently, in cases with monthly and lifetime frequency caps, forecasting can overpredict availability.
Forecasting looks at priority to determine the Reserved by same- or lower-priority line items number--the number of impressions a line item can get if you’re willing to take impressions from same- or lower-priority line items. Priority is also taken into account when calculating impressions likely to deliver.
Forecasting ignores this delivery control. Instead, it optimizes delivery the best it can. For example, if a line item is set to deliver evenly, the forecast simulation might allocate impressions on a frontloaded basis. In some cases, this can lead to overly optimistic forecasts.
Cost is not a criteria considered in forecasts.
When you run a forecast on roadblock ads, DoubleClick for Publishers projects available inventory for all creative sizes in the line item, regardless of whether or not they serve together in a single view.
For example, if you have a line item containing one creative that’s 728x90 and one that’s 300x250, for three page views, forecast results count one impression for a view in which just the 728x90 creative is projected to serve, one for when just the 300x250 is projected to serve, and two for when they’re projected to serve together (the roadblock). The forecasting simulation returns a result of four, which accurately simulates how this line item would serve when live, even though there is only one page in which both the 728x90 and the 300x250 would serve together to the same page.
If you have an ad with multiple creatives of the same size, and you select the As many as possible or One or more setting for displaying creatives, then forecasting can underestimate the available inventory because it currently assumes every ad has only one creative of a given size. For example, if you have an ad that has two 300x250 creatives, and a webpage with two ad slots of that size, the forecast simulation counts one page view as one impression, whereas in reality, both creatives will serve, making two impressions. So in this case you should double the number of available impressions to get an accurate count of how many impressions to safely book.
Example: forecasts on line items with multiple creatives of the same size
The table below details expected forecast results based on the following assumptions:
The website has three pages in the following configuration:
Page one has 3 slots of 300x250
Page two has 2 slots 728x90
Page three has 2 slots of 300x250 and 1 slot of 728x90
Line item delivery is set to "As many as possible."
Creative size(s) No. of creatives Forecast imps Actual imps 300x250 1 2 2 300x250 2 2 4 300x250 3 2 5 300x250, 728x90 1, 1 4 4 300x250, 728x90 2, 2 2+2=4 4+3=7 300x250, 728x90 3, 2 2+2=4 5+3=8
Results on the first page of the forecast provide guidance that can help you decide how many impressions to book. You can also gauge and adjust the effect that booking the prospective line item would have on existing line items by clicking the View contending line items link.