Anne Skeldon was invited to write an Editorial for the journal SLEEP on a paper that uses a mathematical model to analyse sleep in flies (Abhilash & Shafer, 2023). The Editorial,  co-authored by Anne and Derk-Jan Dijk, Director of the Surrey Sleep Research Centre, is now available online (link here). The Editorial highlights some of the problems that arise when fitting models with complex behaviour to data — results critically depend on the assumptions that are made. The figure below, from the Editorial, shows that similar patterns of sleep can be obtained by varying parameters of the model in two different ways with two different physiological interpretations.