In an ideal world, each experiment would have a well motivated independent variable, and everything else would be exactly the same between conditions. Independent variables then are constituted by the difference between student researcher experimental condition and student researcher control condition. A between-subjects design is useful where there is a danger of running into so-called “range effects”. Suppose student researcher are interested in what affects people’s ability to remember a set of faces that they are shown for a brief period. When designing a research project “start simple”, and only introduce complex factorial designs when student researcher have demonstrated robust effects with simpler designs. In the simplest terms, where the behaviour of two (or more) different groups of people is compared, this is a between-subjects design, whereas when a comparison is made of the behaviour of the same group of people under different conditions, this is a within-subject design.