A recent study has provided some insight into how advertisers should optimize their video ads, depending on what message they are trying to communicate, and who they are trying to reach.

The conclusion was that shorter mobile video ads leave a stronger impression on millennial consumers, while older audiences respond better to longer ad spots, according to a new study conducted by Millward Brown Digital and Tremor Video with the backing of the IAB.

“Demographics respond differently to ad lengths. Millennial consumers respond better to 10-second mobile video ads, while consumers aged 35-54 respond better to 30-second shorts. This trend might be driven by the type of content that millennials are consuming on popular social video apps like Snapchat and Vine.”

“Screen size and ad length matter for campaign messaging. 30-second video ads and larger screen sizes tend to do a better job conveying complex information to viewers. When asked how much new information an ad provided, 73% of survey respondents gave higher marks to the 30-second ads, compared to 68% for the 10-second ads. Similarly, 73% of survey respondents claimed that ads viewed on a tablet were good at conveying information, compared to 65% for smartphones. This suggests that screen size matters, and that marketers should make ads that contain complex or new information into longer formats.”

The study is particularly important for businesses looking to reach audiences on mobile video platforms, namely Facebook, Twitter, Snapchat, and Instagram. Each of these platforms has introduced longer video ad formats to allow marketers more time and space to reach consumers.

However, if businesses are trying to engage consumers then these longer ad spots may not work as well, compared to when trying to convey new information to audiences. Consumers are spending more and more time on their mobile devices, which creates a tremendous opportunity for marketers to reach existing and potential customers.

Overall, marketers should take on different mobile approaches depending on the size and demographics of the audience they want to reach and the type of message they want to send. With all tactics, marketers need to respect the personal nature of the mobile device and pay attention to the potential for communication overload.