In my previous post I looked at some of the issues affecting the extent to which ‘big data’ gives a reliable picture of the world around us. In this post I want to take you through one of the least sexy—but most important—parts: the data itself. My point, again, is not to suggest that big data is fatally flawed, but to call into question some of the easy assumptions upon which we rely when working with this type of data, and the universality of the conclusions that we can draw from this type of research.