In the online advertising industry, a viewable impression is a measure of whether a given advert was actually seen by a human being, as opposed to being out of view or served as the result of automated activity. The viewable impression guidelines are administered by the Media Rating Council and require that a minimum of 50% of the pixels in the advertisement were in an in-focus tab on the viewable space of the browser page for at least one continuous second.
The first system to deliver reports based on a viewable impression metric for standard IAB (Interactive Advertising Bureau) Display ad units, called RealVu, was developed by Rich Media Worldwide and accredited by the Media Rating Council on March 9, 2010. Other companies to offer viewable impressions include DMA-Institute OnScroll, C3 Metrics, Comscore, and AdYapper, while MSNBC utilizes ServeView, a proprietary system in use since 2010.
The definition of a viewable impression may depend on the type of the ad units and the reporting system. For example, a viewable impression for ads of pre-defined size delivered to pre-defined space on the content page is registered by RealVu when the ad content is loaded, rendered, and at least 60% of the ad surface area is within the visible area of a viewer's browser window on an in focus web page for at least one second. Click-through is enabled at the moment of the "viewable impression".
Viewable impressions were developed as an improvement of the online impression metrics measured by first ad servers developed in the mid-1990s, which analyze HTTP requests in a server log and cannot provide information on events fired by a viewer’s browser; thus, they cannot measure whether ad content was actually visible to a viewer.
Overview
With the development of the first ad servers in 1995–1996 the assumption was that a requested ad was always available to the viewer of a requested web page. This allowed for the utilization of the server log file for collection of metadata to deliver a metric called the Online Impression that in traditional media meant an impression on a viewer.
This type of advertising metric was meant to resemble Television and print advertising methods for speculating the cost of an advertisement, with the promise of even more accuracy due to the interactive nature of the Internet eliminating the need for industry-accepted approximates such as Nielsen ratings for television and circulation figures for print publications.
The value of an ad traditionally was based upon an estimate of how many different people saw or heard the ad. The following are current accepted means of calculating CPM for different mediums: 1. CPM for print media (when audience data is available):
2. CPM for broadcast media:
With the advent of the Internet, through log file server collecting data it was believed that ad views could be tracked with unprecedented accuracy and “number of different prospects reached” was removed from the equation, and a new CPM equation was created for the internet:
3. CPM for the Internet:
However the assumption that an ad requested from an ad server is always visible when the viewer is on the requested page was wrong because of a few technical reasons and the fact that the web page is usually longer than the height of a computer screen. Eventually it became apparent that a large number of ad impressions measured for CPM pricing actually never rendered in the visible area of a viewer’s browser screen.
CPMV (cost per thousand viewable ads) Until 2010 it was very common for large publishers to charge for most of their advertising inventory on a CPM or CPT basis. A related term, effective cost per mille (eCPM), is used to measure the effectiveness of advertising inventory sold (by the publisher) via a CPC, CPA, or CPT basis.
Partially to avoid the limitations of server side impression methodology many models emerged that were based on direct response: CPC - Cost per click Through CPL - Cost per lead (lead usually meaning a free registration) CPS - Cost per sale dCPM - Dynamic CPM CPA – Cost per action