The Lean model would be the most useful method for reducing waiting times. A number of quality improvement models that apply rigorous processes to identify, measure, and correct areas in need of improvement are in use by health care systems. Understanding the appropriate application of these models is important in achieving optimal quality improvement outcomes. The Lean model is a quality improvement method that focuses on eliminating non–value-added activities, or waste, within a system. Lean uses value stream mapping, a tool that graphically displays the steps of a process and the time required for each step from beginning to end. This allows identification of steps in the process that may be problematic. The Lean model is particularly well suited for analyzing apparent inefficient or redundant processes, such as prolonged waiting times, by identifying where in the system the delays are occurring.

The Define, Measure, Analyze, Improve, Control (DMAIC) process is a five-step approach used within the Six Sigma model, a quality improvement model initially developed to improve industrial manufacturing quality that has since been adapted to optimize health care system function. It tends to focus more on quality control in each step of a process rather than on optimizing the overall efficiency of a system.

Plan, Do, Study, Act (PDSA) cycles are rapid tests of change in which baseline data are collected, an intervention is planned and then implemented on a small scale, the results are analyzed, and an action plan is made. PDSA cycles tend to focus on specific points in a system and are not typically used for studying overall system function and efficiency.

Six Sigma is a quality improvement model that is designed to reduce variation and drive a process toward near perfection. The name Six Sigma is derived from a statistical measure indicating the number of standard deviations from the mean in which no production defects occur. Thus, a Six Sigma measure indicates almost perfect production quality. Several practical methodologies that are oriented toward the quality of each step in a process are used within Six Sigma. As an example, an ICU may have an unacceptably high rate of infections; the Six Sigma model could be used to decrease the defect (infection) rate. Because Six Sigma is highly focused on the quality of each step in a process, it would not be optimal for evaluating factors leading to system inefficiencies, such as patient waiting times.