by Laurie Sullivan @lauriesullivan, December 4, 2014

As marketers become more aware that Web site visitors never see many of the ads served on publisher sites, verifying that someone actually saw the online advertisement becomes a greater concern. Since an ad served does not necessarily equal an ad viewed, Google conducted a study of its display advertising platforms Google and DoubleClick, which revealed that 56.1% of all impressions Google measured in a recent study were not seen, and the average publisher's viewability rate came in at 50.2%.

Google conducted research using its Active View technology to learn about the current state of viewable impressions on the Web. It reveals five factors that affect the extent to which ads are seen.

A viewable impression occurs when 50% of an ad's pixels are on screen for one second, per the Media Rating Council and the Interactive Advertising Bureau. The data used in Google's study is based on display ads in desktop and mobile browsers, and does not include mobile in-app or video ads. The data was collected in July 2014 and October 2014.

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The research finds that the most viewable position is right above the fold, not at the top of the page. The most viewable ad sizes are vertical units, and page position is not always the best indicator of viewability.

Not all above-the-fold impressions are viewable, while many below-the-fold impressions are seen. Median viewability for above-the-fold ad units is 68%, whereas median viewability for below-the-fold ad units is 40%.

Viewability varies across industries. The highest viewability rate typically belongs to the sites with more captive engagement.

Finance has a viewability rating of 43.6%, travel, 42.6%; home and garden, 42.5%; beauty and fitness, 42.3%; law and government, 42.2%; world localities, 42.0%; auto and vehicles, 41.9%; book and literature. 41.5%; and shopping, 40.8%. Reference sites hold the highest at 51.9%; compared with online communications at 48.9%; and games at 48.4%. From there it drops to people and society at 43.6%.

While the viewabiity rate ranges across content, verticals and industries, the content that holds a user's attention has the highest viewability rating, per Google.

Less than 12% of publisher sites have viewability rates of 30% or less in Google's and DoubleClick's display network, per the findings.