I've just finished reading a book called "Everybody Lies". The hypothesis is that people control what they put on their social media accounts, lie to pollsters, present an 'image', but they are honest in their Google searches. So, for example, when he analysed the results of what people actually searched for, they discovered that Democrats in the USA are as likely to be racist as Republicans.(I don't want to put the search terms here, they were offensive). I was surprised at some of the results and think that's an interesting concept, which I'm sure will be exploited by political parties soon.
It was written by an economist, who used to work at Google as a data scientist, so I'm assuming he's reliable.