Everybody's doing it – no self-respecting media plan is complete without the budget allocation to digital advertising. Whether you're selling packaged goods or fast food, autos or insurance, you've got to be there. And it's not just about driving prospective buyers to your site anymore – it's about brand building and continuing the conversation with consumers.

So you've made the investment in online advertising... what should you expect it to add to your overall communications program? Can your digital campaign stand on its own, or does it need to be surrounded with the more traditional, broad-based media to achieve optimal results?

Despite all the hype, even the most robust digital campaign will almost never achieve the breadth of advertising awareness that is characteristic of TV and other traditional offline media. One of the strengths of digital media, namely the greater ability to pinpoint specific targets, can also be a weakness. Communicus findings across a broad range of product categories show that digital campaigns only add an average of 2% of exclusive branded awareness to a multimedia campaign.

Moreover, our findings indicate that digital campaigns are better at generating awareness among brand users than are TV campaigns. TV campaigns, on the other hand, generally do a better job of conveying your brand story to those who aren't already among your users or 'brand fans'.

For example, the composition of the group of teens who had branded proved awareness of a recent television campaign for a major candy brand included 16% of teens who were already (before seeing the advertising) regular users of the brand. In contrast, the group with branded proved awareness of the digital campaign included 35% – or over twice as many – brand users.

One of the most crucial dynamics that differentiates digital advertising from other, more traditional paid advertising media is that the audience has to want to engage with a particular digital ad. Digital is a 'lean forward' medium; it is more about conscious choices about what to pay attention to, or not, than the more passive, 'lean back' media like TV. This applies to 'traditional' digital media such as banner ads, and is even more manifest in Branded Social Media – which involve taking specific actions to engage with the brand communications.

Communicus research strongly suggests that people are more likely to 'lean into' or choose to engage with your digital campaign if they've already learned, through exposure to advertising in other media, that there's something relevant or rewarding to be gained. So, your online campaign will generally work best among those who've also engaged with other broad-based media within your campaign. As a corollary to this, we have found that it is extremely difficult for a digital-only campaign to achieve the kind of engagement that you can accomplish with a digital campaign that's a part of something bigger.

Think about if you saw a talking baby on the side of your screen right now. Earlier this week you saw a hilarious E*Trade commercial, so you are more likely to pay attention to – and maybe even click on – the talking baby. Or, if you saw a box with the PC guy and the Mac guy as a digital ad, you might click on it to hear their conversation, but only because you're familiar with the TV campaign and find those ads to be entertaining.

As these examples imply, for a digital campaign to be most effective as part of a multimedia campaign it should be creatively synergistic with the other, offline media. This is not to say that the digital campaign needs to exactly replicate the TV campaign (any more than taking a frame from your TV execution would necessarily create the best magazine ad). The key to using offline and online media synergistically lies in having linkages that enable the consumer to recognize the ads in the different media as being part of the same brand story while using each medium to its greatest unique advantage.

So what does digital advertising bring to the party? Besides being extremely efficient and targetable, online media can help to further consumer conversations with your brand. But, parties are no fun with just one guest; and digital on its own has trouble bringing in new people to your brand and is generally most effective in concert with, but not as a substitute for, offline media.