Admittedly, the ADP report comes from a much smaller subset of data derived 500, 000 business employing over 21 million workers, while the government statistics aim to encompass the entire workforce.
To achieve this, the company needed to run complex data mining models on a large volume of data, which took at least three weeks of processing time, even with a subset of the 2.8-petabyte data set.
Some app designers, like game developer Zynga, have signed up millions of users despite the opt-in requirement, but many operators end up with data describing only a small subset of their users.