Editor’s note: Jeri Smith is president and CEO of Communicus Inc., a Tucson, Ariz., research firm.

Why is it that some individuals choose to engage with a particular ad while others ignore it all together? That’s the million-dollar question. Creators of advertisements strive to ensure that their ads secure the attention of the widest possible swath of consumers within their target audience. With that said, not all consumers are created equal when it comes to the likelihood of engaging with a specific ad for which they have exposure opportunity.

Kraft Mac & CheeseThis important yet little-researched area within the field of in-market advertising effectiveness involves evaluating how pre-existing consumer brand experiences and beliefs affect engagement with advertising. Generally, individuals who already admire a brand will be more likely to engage with ads for that brand. It makes sense that this would be true – individuals who are already considering shopping for a BMW are more likely to engage with BMW ads than individuals who are not. The phenomenon stands true for less considered purchases as well: Tide detergent customers watch Tide commercials and Kraft Macaroni & Cheese fans pay closer attention to Kraft Mac & Cheese ads. It’s reinforcing to hear (via TV or video) how smart you are for considering buying a BMW, for your choice of Tide or Kraft Macaroni & Cheese.

In connection with this dynamic, most advertisers and researchers realize that you can’t presume advertising impact by comparing brand metrics between those who have seen your ads with the same metrics among those who haven’t. Predictably, brand metrics will be stronger among the ad-aware but this is generally discounted – with the reason being the aforementioned phenomenon.

This phenomenon is called selective perception. The strength of selective perception varies by brand as well as by the particular creative approach employed in the ads for that brand. Depending on whether a brand has a frequency or loyalty-building objective, or an awareness, trial, market share expansion strategy, selective perception can be positive (in the former case) or a hurdle to be overcome (in the latter case).

It’s important to be able to measure and understand the relative degree of selective perception for a particular campaign to determine the success in communication and persuasion beyond the brand’s base of user fans. So how does one measure how consumers feel before engaging with ­– or ignoring – an ad to which they have exposure opportunity in the real world?

One method is to utilize longitudinal design research – interviewing the same panel of consumers before and after an advertising campaign runs in-market. In the pre-wave, researchers survey a target audience sample before the campaign appears in-market – collecting brand usage and preference data for a range of brands within a product category. In the post phase, researchers question the same respondents on what advertising they have viewed recently. Researchers then compare advertising recall among respondents who were brand users or fans in the pre-wave versus those who weren’t.

Perhaps you’ve discovered strong selective perception for your brand’s campaign – maybe brand fans are twice as likely as non-fans to engage with the TV executions within the campaign. But to achieve its marketing objectives, this advertising campaign needs to engage non-fans as well. A closer examination via qualitative research or by employing new biometric measurement approaches can help to illuminate particular elements within the ads that are of interest to non-fans. Additionally, brands can initiate additional research to identify the types of triggers that will cause non-fans to engage with ads for their brand. These insights can be used to ensure that non-fans are engaged by the brand’s campaign – to learn something new and to perhaps change their way of thinking or even their purchase intentions.

Unless a brand is able to identify the selective perception dynamic, it can be a mystery as to why, despite its strong copy testing or broad-based in-market tracking results, a campaign is failing to generate the trial or expansion of household penetration that the advertising is charged with achieving.

The selective perception phenomenon is present across many media types beyond TV and video, and is even more prevalent in digital and online consumer-brand interactions. Further, we know that having engaged with an ad for your brand in one medium, a consumer may be more inclined to notice ads within the same campaign in other media. As such, an understanding of selective perception across media types can lead to superior insights about how to make the overall campaign work harder for your brand.

It’s a relatively simple matter to evaluate and diagnose the selective perception dynamic for a particular campaign. Researchers who don’t attend to this practice are missing important insights that can be highly actionable to the advertisers whose campaigns we are helping to optimize.