Brands are investing more in online-video campaigns, but there's still no clear consensus about how best to assess video ads' effectiveness, this article notes. Metrics such as completion rates and brand lift are gaining acceptance but are easily skewed by factors such as video length, ad-screening time and the context in which the video is displayed. "A plethora of factors will color the results of any single metric, such as completion rate, for a specific campaign," the article warns.