Cambridge Analytica kept Facebook data models through US election

Facebook's failure to compel Cambridge Analytica to delete all traces of data from its servers – including any "derivatives" – enabled the company to retain predictive models derived from millions of social media profiles throughout the US presidential election, the Guardian can reveal. Leaked emails reveal that when Cambridge Analytica told Facebook almost a year before the election that it had deleted data harvested from tens of millions of Facebook users, it stopped short of agreeing to also erase derivatives of the data. The correspondence, obtained by the Guardian, also raises questions about the accuracy of the testimony that Facebook's chief executive, Mark Zuckerberg, gave to the US Congress last month. Derivatives of data, which can include predictive models, or clusters of populations in psychological groupings, can be highly valuable to companies involved in micro-targeting advertisements to voters. Data scientists say such models and analysis are often more valuable than underlying raw data.