 Popper draws a clear distinction between the logic of falsifiability and its applied methodology. The logic of his theory is utterly simple: a universal statement is falsified by a single genuine counter-instance. Methodologically, however, the situation is complex: decisions about whether to accept an apparently falsifying observation as an actual falsification can be problematic, as observational bias and measurement error, for example, can yield results which are only apparently incompatible with the theory under scrutiny.