Imagine if six out of ten billboards were behind trees or buildings, or were facing the wrong way. It would look ridiculous and no sane advertiser would buy those billboards. Yet, according to a new report by ad management platform Vindico, that’s effectively what’s happening with online video ads.

After analyzing 3.9 billion video ad impressions in September and October, 2013, Vindico found that 57 percent of them don’t have an opportunity to be seen by a viewer. “Viewability” to Vindico means that 50 percent of the ad is in view for at least one second.

Vindico found that viewability ratings varied by the type of website. Major media sites got the highest scores for viewability. Some major media sites offered triple the viewability of other sites.

Poor viewability is wasting ad dollars, Vindico says, adding that non-viewable impressions increase CPM costs by 133 percent.

“Online video advertising is a young and quickly growing space,” says Matt Timothy, president of Vindico. “What these findings show is that we’re building that space on a rickety foundation. We as an industry need to start behaving more like our counterparts in television in terms of quality, and create a sustainable, healthy industry and a clear path for brand investment.”