Like a carton of milk, campaign data eventually expires.

While carrying out ad campaigns, marketers and their vendors often collect demographic, behavioral, location and purchase data about the users they serve ads to. This data can be reused by marketers to retarget ads and inform the key performance indicators they choose for ensuing campaigns. But eventually the data becomes outdated and inaccurate.

In an April survey of US marketers conducted by LoopMe and Sapio Research, about half considered data reliable to utilize in ad campaigns for one to two years. Less than one-third said data is usable after two years. On average, respondents felt data is reliable for campaign use for 1.9 years.

The surveyed marketers said that they find demographic and financial data to be the most valuable, while device ID and cookies are thought to be the least valuable.

Part of the reason why user data becomes unreliable after a few years is because the types of ad formats and metrics that advertisers rely on changes from year to year, according to Brendan Gahan, founder of ad agency Epic Signal.

“Things change so fast in this industry,” he said. "Not just from an advertising technology standpoint, but from brands’ own priorities and internal processes. You have to continually adapt your approach to data and where its value lies.”

The survey also gives some insight into how marketers approach data storage.

To manage audience data, marketers often rely on data management platforms (DMPs). According to a January survey of US ad and marketing professionals conducted by Advertiser Perceptions, ad inventory discovery is the top criterion that drives DMP selection.

Want to learn more about how campaign data is being used by advertisers today? Check out our recent report on ad targeting.