We analyzed data from millions of anonymized set-top boxes to compare how different ad lengths impact the number of impressions (views) an ad receives. The chart below shows four different ad lengths along the horizontal x-axis (15-, 30-, 45- and 60-second) with the corresponding level of impressions on the vertical y-axis ("Baseline Impressions" represents the number of impressions received by a 15-second ad):
This analysis shows that a 60-second ad reaches only about 4% more viewers than a 15-second ad. Therefore, a longer ad doesn't necessarily buy more viewers -- it buys roughly the same viewers, but for more time.
If you have a complex message, you can use longer ads to engage viewers for a greater period of time. But if you want to maximize reach with a less complex message, you'll benefit from spreading out more frequent, shorter ads.
Posted by Dan Zigmond, Technical Lead for Google TV Ads
Link - from Let's Take it Offline
Related: Join us at the ERA Annual Convention in Las Vegas Creating an Effective Print Ad