Wow. Nielsen recently compared their survey data with actual usage data to measure quarterly video viewing on phones & tablets.
According to the survey data, people watched 5 hours 23 minutes of video in Q4 2013. According to the Electronic Mobile Measurement tool (which measures actual mobile usage), people watched 1 hour 23 minutes. That's right, survey data overstates this by something like 500%.
Two quick lessons emerge:
1. People are clearly overstating how much video they're watching on their phones & tablets. So adjust down with numbers you see.
2. We should, as always, be very cautious about relying on self-reported survey data for measuring people's behavior. Surveys are great at measuring beliefs, though--which are just as important. But this makes me wonder how people really use their mobile phone while shopping, for instance, vs. what they might say in a survey.