Summary
Objectives: Use of Shewhart control charts in quality improvement (QI) initiatives is increasing.
These charts are typically used in one or more phases of the Plan Do Study Act (PDSA)
cycle to monitor summaries of process and outcome data, abstracted from clinical information
systems, over time. We summarize methodological criteria of Shewhart control charts
and investigate adherence of published QI studies to these criteria.
Methods: We searched Medline, Embase and CINAHL for studies using Shewhart control charts
in QI processes in direct patient care. We extracted methodological criteria for Shewhart
control charts, and for the use of these charts in PDSA cycles, from textbooks and
methodological literature.
Results: We included 34 studies, presenting 64 control charts of which 40 control charts plotted
two phases of the PDSA cycle. The criterion to use 10–35 data points in a control
chart was least adhered to (48.4% non-adherence). Other criteria were: transformation
of the data in case of a skewed distribution (43.7% non adherence), when comparing
data from two phases of the PDSA cycle the Plan phase (the first phase) needs to be
stable (40.0% non-adherence), using a maximum of four different rules to detect special
cause variation (14.1% non-adherence), and setting control limits at three standard
deviations from the mean (all control charts adhered).
Conclusion: There is room for improvement with regard to the methodological construction of Shewhart
control charts used in QI processes. Higher adherence to all methodological criteria
will decrease the risk of incorrect conclusions about the process being monitored.
Keywords
Statistical process control - healthcare quality improvement - quality improvement
methodologies - process assessment (health care)
