Anxiety and depression: why and how to measure their separate effects.

It is well recognized that depression and anxiety are closely associated, but nonetheless, they may be associated with distinct causes and consequences. For example, anxiety and depression are associated with different effects on information processing. This paper argues that experiments should not study anxiety or depression in isolation, but should measure both variables. It is argued that this methodological step is both important and commonly overlooked. Even when both depression and anxiety are measured, methodological difficulties can confuse their effects. Common difficulties in choice of measures and in participant selection criteria are discussed, and recommendations are made for overcoming them. The argument is made drawing from illustrations within the experimental cognitive literature, but conclusions and recommendations are equally applicable outside this area.