Story highlights Cambridge Analytica is crunching data for the Trump campaign

They use personality tests and voting records to create tailored political ads

London (CNN) In a non-descript office in central London, young analytical minds are hard at work crunching thousands of pieces of data about every American adult.

They are Donald Trump's secret political weapon. His campaign paid more than $5 million in September alone to Cambridge Analytica, which claims it can convince voters to back him by tailoring Trump's political ads to their personalities.

Their approach combines micro-targeting, already in use in political campaigning, with psychological profiling. The company gathers up to 5,000 pieces of data about a potential voter to create a psychological profile, then adapts political ads to his or her personality and beliefs.

Using a survey usually placed on social media, the company invites users to take a personality test. The results of that test help the company group people under personality types measuring openness, conscientiousness, extraversion, agreeableness and neuroticism.

Data-crunchers then combine individuals' personalities with their voting history, where they shop, what they buy -- even what they watch on television.

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