Process improvement - six sigma

Six Sigma

What is Six Sigma?

Six Sigma is a quality improvement model originally developed by Motorola in 1985. The goal of Six Sigma is twofold: find and remove defects in processes, and develop processes that are carried out the same way each and every time in order to decrease variation. Sigma is defined as standard deviation. Six Sigma represents the three standard deviations above and below the mean also known as upper and lower control limits. A process is considered to be in control when statistical analysis shows variability occurring within these 3 standard deviations above and below the mean, resulting in an extremely low defect rate. This reflects a tightly controlled process with a little variation that is out of the norm. 

How Does Six Sigma Work?

The roadmap used by Six Sigma is a set of problem-solving steps known as DMAIC: Define, Measure, Analyze, Improve and Control. See below for a further explanation of each step: 

  • Define- the team, variable and baseline data, goal to reach once variation is reduced, and project schedule 
  • Measure- assess baseline data, decide what is going to be measured in moving forward and who will do that. This may include using Pareto and process control charts. 
  • Analyze- review data to identify themes and determine causes for errors. Tools that may be useful in this step include control charts and fishbone diagrams.
  • Improve- Develop solutions to reduce variation. Trial these solutions on a small scale. 
  • Control- Develop ways to sustain the initiative over time. This may include continued monitoring of data and employee education- initial, periodic refresher, and built into orientation for new employees (Kelly, 2018) 

Case Example

North Shore University Hospital (NSUH) in Manhasset, NY used Six Sigma to reduce bed turnaround time (TAT) for admitted patients.  TAT was defined as the time a patient received discharge instructions to the time the admission RN was notified that a clean bed was available. 

The initial quality improvement focus was on one surgical unit that accepted patients from the ED, Critical Care, and PACU. The problems identified included communication among team members, inefficient processes, the role of environmental services, and a discrepancy among who was supposed to control the process versus who actually was controlling the process. Opportunities for improved communication between RN’s and other team members were identified. Admission RN’s were using an inefficient, time-consuming process to determine the availability of a clean bed. This included conducting unit rounds, phone calls, and reviewing census information. The bed tracking system (BTS) measured the role that environmental services played. Prior to this project, it was felt that environmental services significantly contributed to delays in TAT. In fact, data review showed that the average time from patient discharge to the room being cleaned was 55 minutes, exceeding the national standard. Lastly, the clerical support associate controlled the process, however, according to policy, this was not their responsibility. 

Applying the DMAIC steps to this problem looked like this: 

  • Define-The QI focus was TAT, beginning with the time a patient received discharge instructions to the time the admission RN was notified that a clean bed was available. A target of 120 minutes was established for a goal, with an upper limit of 150 minutes.
  • Measure– a process map was used to identify steps in the process. The time required for each step was tracked using a data collection sheet. Baseline data was obtained to determine the current TAT was 226 minutes 
  • Analyze– The data was broken down into patients that were discharged home versus transferred to rehabilitation.  The team decided to evaluate and measure only patients that were discharged because more factors were within the hospital’s control with this subgroup. Data was analyzed using statistical measures (analysis of variance and a two-sample t-test). Technical and communication opportunities were identified. Incorrect use of the BTS, along with a lack of communication between care team members and the admission RN regarding clean bed status, were creating delays in the process.  
  • Improve– The team brainstormed solutions that included the following: 
    • Re-education on the BTS, integrated into orientation and annual competency
    • System changes- visual aids showing communication occurred between RN and care team members,  bedside BTS cheat sheets, admission RN beeper system with connection to the BTS, allowing for instant notification of a clean bed status
    • The mean TAT was reduced from 226 minutes to 90 minutes. 
  • Control – data was monitored on a monthly basis, showing continued improvement (Pellicone & Martocci, 2006)

In summary, Six Sigma provides a step-wise approach to breaking down a problem, identifying errors or defects, and reducing variation in processes. 


Kelly, P., Vottero, B. A., & Christie-McAuliffe, C. A. (2018). Introduction to quality and safety education for nurses: Core competencies for nursing leadership and management. Springer Publishing Company.

Pellicone, A. & Martocci, M. (2006). Faster Turnaround Time. Quality Progress, 31-36.

Copyright by Jeanette Zocco MSN, RNC-OB, C-EFM, C-ONQS

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