What is six sigma? How does it apply to health care?

There are two meanings 1) Sigma ( σ ) is the accepted symbol for 1 standard deviation from the mean of the “normal” distribution (bell curve).  Since 1 sigma would exclude 31.8% of a normally distributed event under consideration and three sigma would exclude 0.3%, six sigma implies events of very low frequency (on the order of 3 per million). 2) Six sigma is also commonly used as the name of a process of quality control originally developed at Motorola Corporation and later adopted by many including General Electric Company (a six sigma error rate is considered to be virtually flawless).  In many industries application of the methodology has reduced defects, improved customer satisfaction, and decreased costs.  With respect to medicine, Parker et al used these techniques to develop a process that improved adherence for antibiotic prophylaxis in patients undergoing cardiac surgery (1); Women and Children’s hospital of Charleston used six sigma to enhance access to care by decreasing time to appointment and waiting time to see a doctor, increase patient satisfaction, and improve revenues in a resident run obstetrics and gynecology clinic (2); and Massachusetts General Hospital avoided the addition of an additional shift for its proton beam facility by changing how it scheduled cases requiring anesthesiologists (3).  Key to the success of this methodology is the fact that it is data driven.  It focuses on process improvement and variation reduction using the paradigm of define, measure, analyze, improve, and control (4).  It can be applied to both existing and planned processes.  We do not like to consider our practice of medicine to be the same as manufacturing super soaker recreational water guns.  However for success both require the correct application of a sequence of steps.  In the case of medicine  failure of any one of those steps may lead to patient injury, patient or family dissatisfaction or increased costs in the form of a cancelled case, increased hospital stay, etc.

1)      Parker BM et al: Six sigma methodology can be used to improve adherence for antibiotic prophylaxis in patients undergoing cardiac surgery.  Anesth Analg 2997:104:140-6

2)      Calhoun BC: Six-sigma inspired workflow redesign enhances access to care and increases patient satisfaction, visits, and revenues in obstetrics and gynecology residency clinic.  (http://www.innovations.ahrq.gov/content.aspx?id=1868 )

3)      Krasner J: New medicine for what ails hospitals.  Boston Globe January 28, 2008 (http://www.boston.com/business/healthcare/articles/2008/01/28/new_medicine_for_what_ails_hospitals? )

4)      Sivy J: Six Sigma.  Carnegie Mellon Software Engineering Institute Software Technology Roadmap (http://www.sei.cmu.edu/str/descriptions/sigma6_body.html )

David S. Smith, M.D., Ph.D.