Evaluating improvement.

Evaluating quality improvement interventions requires a variety of methods. These range from quantitative methods, such as randomised controlled trials, to quasi-experimental (controlled before-and-after and interrupted time series) and uncontrolled before-and-after studies, including clinical audits, to determine whether improvement interventions have had an effect. Qualitative methods are often also used to understand how or why an intervention was successful and which components of a complex or multifaceted intervention were most effective. Finally, mixed methods designs such as action research or case study methods are widely used to design and evaluate improvement interventions.