Twitter announced the addition of aggregate user age information to the Audience API (application-programming interface) from Gnip.
Aggregate user age information became the 11th demographic model available for audience analysis, joining:

Gender
Language
Interests
TV genre
TV show
Location (country)
Location (region)
Location (metro)
Device category
Wireless device network

Mark Callahan, who works on data product marketing for Twitter, added in a blog post:
Twitter?s age models use a blend of several data sources. Many users provide birthday information in their profile settings. For those that don?t, we apply other proprietary signals such as the accounts that users follow or the tweets they engage with. We?ve also evaluated the accuracy of our models with data from industry-leading third-party partners in order to ensure that they meet the needs of our customers. Just as was the case with the Audience API?s 10 original user models, we worked diligently to protect individual user privacy throughout the process of surfacing aggregate age data. We are now able to share incredibly valuable data about the age clustering of any audience that you may want to explore on Twitter while simultaneously protecting against any one individual user?s information being revealed.
Twitter advertisers: What do you think"

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