For more than a century, advertisers have complained about the unscientific nature of their business by repeating the famous words attributed to 19th century department store mogul John Wanamaker: “Half the money I spend on advertising is wasted; the trouble is, I don’t know which half.”

Finally, in the second decade of the 21st century, we can answer Wanamaker’s question, says CBS research guru David Poltrack. With new technology, measurement services such as TRA, Nielsen Catalina and Nielsen MBI can quantify the “the amount of your product that was consumed by people before they saw your ad and the amount consumed after they saw your ad. They can document the return from the advertising.”

The impact of this development on TV advertising can’t be overestimated. “It’s is something advertisers have always wanted,” Poltrack says. “Financial management has always put pressure on marketing departments to measure the value of investments in advertising, and now for the first time we can do that with precision.”

How? Measurement services collect data from millions of set-top boxes and compare viewing behavior with information about what those same households actually buy, gathered via shopper cards. The method — single-source measurement — gauges TV viewing and product consumption of the same household.

“This allows us to go back to an advertiser and say, ‘you sold X hundred thousand more tubes of toothpaste to people who saw your ads than to people who didn’t,’” says Poltrack. “It answers the Wanamaker question.”

More than that, Poltrack adds, it allows advertisers to zero in at the program level and see which TV shows are working for their products, and even which creative is best, and make adjustments to increase its effectiveness.

Consumers agree to share their information when they get their shopper cards but, says Poltrack. Privacy remains protected through “double blind matching,” which maintains two databases — viewing and shopping — that are merged only after identifying data is stripped away.

Poltrack is a panelist at Massive: The Advertising Summit, taking place June 6 in Hollywood. It is co-sponsored by Variety and Rogers & Cowan. Several speakers espouse innovative approaches to the fast-changing ad biz.

Uwe Gutschow, VP of digital at ad agency Innocean USA, believes in messages that “are part of what people are interested in rather than interrupting it.” Innocean, he says, engages consumers by pulling off stunts such as getting Walking Dead writer Robert Kirkman involved in creating a “zombie survival car” (pictured), unveiled at last year’s Comic-Con.

“We didn’t interrupt sponsorships elsewhere,” Gutschow says. “We added value and created talkworthiness around the vehicle.” The car’s fictitious owners manual, published in a limited edition, now fetches $1,500 on eBay.

Digital brings the best of all worlds to advertisers, says Jordan Levin, former WB topper and co-founder of digital content company Generate. “At the WB there were two ways to engage with a TV audience: passive ad inventory and integration opportunities with the content. Digital affords both of these, plus the social media layer allows for real engagement activity.”

That activity is crucial for reaching younger consumers. “You can still reach 35-plus with TV, but it’s starting to change permanently,” Levin says. “If you want to reach under-35, you can’t do it on TV alone anymore.”