While the preceding chapter discussed the origins of evidentiary bias that arise from the pursuit of political interests within a fundamentally competitive policy arena, this chapter explores a second, less immediately observable, origin of bias. Here we particularly draw on the field of cognitive psychology to explore the ways in which common, yet often unconscious, mental processes may also induce technical and issue bias. As will be shown, many of these instances can be directly linked to our existing values and beliefs, thus making them political in origin. Yet these biases may be less easily recognisable than those explored in the previous chapter and can thus be termed the subtle politics of evidence.