A round-up report from eMarketer, specializing in mobile advertising, recently landed in my inbox. On page three, a table of completion rates for U.S. digital pre-roll caught my eye. It claimed that, on average, completion rates for pre-roll ads on smartphones was 77 percent, rising slightly to 79 percent on tablet.

By themselves these stats seem pretty unremarkable—depending on the creative, 70 percent to 80 percent completion rate is a fairly standard result for a non-skippable pre-roll campaign. But there's the catch: unremarkable for a non-skippable campaign.

The vast majority of brands and advertisers understand the difference between a non-skippable pre-roll, which obliges a user to watch an ad before viewing video content, or a skippable format, which allows the user to decide whether or not to watch the ad. What is perhaps less well understood is the difference in performance across KPIs that these two buying options will deliver. A non-skippable pre-roll can achieve the highs of 80 percent completion pretty easily (after all, how many people abandon watching a video because of a 15-second ad?) whereas a very successful skippable pre-roll would be looking at a 40 percent completion rate.

This does not mean that the skippable pre-roll is delivering poor results, although seeing them side-by-side in an Excel spreadsheet might make a junior planner very nervous.

There are arguments for using both types of advertising—skippable ads are far more user-friendly, and the people who do watch your ad are probably genuinely interested in the message, unlike users who cannot skip and merely want to watch the video content after the trailer. On the other hand, non-skippable ads do mean more people see your message and, on average, this type of advertising tends to be cheaper.

The issue occurs when people try to compare the two types directly and the conversation becomes "why has one provider delivered 40 percent completion while another has hit 70 percent?" Both may be delivering pre-roll, but they are very different offerings. The situation becomes even more muddied when campaigns are rolled out across a variety of mobile video formats. For example, native video normally pulls in a completion rate between 20 percent and 30 percent.

What all of this boils down to is what makes each view valuable to each brand, for a specific campaign. There is a key lesson to learn—a high completion rate does not mean a campaign has been successful, and a low one does not mean it was bad. Campaigns should be judged on how they have contributed to the wider marketing initiative.

If the goal is to raise awareness among a specific audience, then a skippable format, which allows users to decide if they are interested, will be more valuable, even if the overall completion rate is lower. Another campaign, looking at reaching as many people as possible, regardless off their initial interest, might see more value in a non-skip campaign. However, it's important to remember that non-skip campaigns can irritate users, and as we know, users are becoming more vocal as to what they will and will not accept in advertising.

The important thing for us as an industry is to stop communicating statistics that do not clearly explain what they are measuring, and for agencies and brands to accept that a high number does not actually represent the best value for money. After all, the point of a view is to improve brand metrics or sales, not to be viewed just for the sake of it.

Stephen Upstone (@stephenupstone) is CEO and co-founder of LoopMe, a unifying platform for all mobile video ad formats.