The way people handle it is to triangulate on the value based on a couple different sources. For example, you may test your TV ad in a handful of markets first

The way people handle it is to triangulate on the value based on a couple different sources. For example, you may test your TV ad in a handful of markets first and see if you experience lift in those areas. In addition, you may offer a unique coupon/promo code in that ad and measure uptake. Then you survey customers and ask them how they heard about you. So maybe in your test regions you saw 2% promo uptake, 3% lift, and 5% survey responses saying they saw the ad. You'll pick an estimate somewhere from 2-5% depending on how conservative or aggressive you want to be. That's how you approach it at a small to medium sized company that actually cares about how their marketing budget is spent. I've also seen an ad agency attempt to measure incremental website traffic gain in the test regions during the time slots the ad aired. If your traffic is large enough to have a clean baseline or the ad response is massive this is probably okay, but I'm skeptical of this methodology. If you're a bigger company, there are also ways to get better viewthru conversion metrics. Shazam offers something to this effect, where they allow you to Shazam a commercial. Shazam can then tell you of people who viewed the commercial who went on to convert. Nielsen may sell this too. With TV if you can't get the numbers to work on a pure customer acquisition basis, you'll measure brand recognition and recall in your test regions. If your ad makes an impact there you can then justify spending some of your brand budget in addition to the marketing budget to justify the overall expense.