The Viewpoint by Martin Marshall and colleagues (Feb 2, p 419) on the science of improvement is welcome and timely. Many improvement methods derive from W Edwards Deming's work. A closer reading of Deming's work reveals his System of Profound Knowledge (SPK) describing four areas: epistemology (how a person's actions are affected by what they deem meaningful knowledge), variation (application of predictive statistics), systems (how parts of a process create a whole system), and psychology (the effect of interpersonal and social structures on a system). These areas cover a range of scientific disciplines, and many will recognise the connections between them and the disciplines brought together under health services research. This framework does not feel narrow and restrictive, as Marshall and colleagues argue. However, we agree there is room for expansion."