Control Charts: The Linkage That Makes Improvement Projects Continuous

It is common to find continuous improvement, CI, projects in social service agencies that are not continuous. These un-linked projects are inconsistent in scope, appear randomly on the calendar, and follow disjointed goals. CI projects are series of projects designed to achieve incrementally higher performance, a service with zero defect. These linked projects require a construct to indicate that the service process is getting out of control. Control Charts are such a mechanism.

While the results of an improved service process still show variability around average performance, common cause variability is controllable. Variations from special and less controllable causes are essentially designed out in CI projects.

Constructing a Control Chart

The construction of a type of Control Chart will be demonstrated on an agency’s drive for excellence in providing high-quality long-term human services. Elderly waiver services are available to medical assistance eligible 65+ residents of a county. Long-term services or LTS allow elderly residents to age-in-place and avoid the more costly nursing home alternative. A quality performance measure applied to the delivery process is the length of time to complete an assessment. The current statutory standard states that at least 71% of assessment documentation be completed within 20 days. Inversely, a defective result is an assessment that exceeded 20 days to complete.

LTS workers of Midwest Social Services successfully completed their first CI project on services they deliver. They have isolated special causes affecting LTS and have minimized any remaining month-to-month variability from common controllable causes. While their long-term goal was to provide a defect-free LTS service, they settled for a goal of 20% defect in the current CI project, the best compromise. This performance level is an improvement over the standard of 29% percent defects. The agency’s improved LTS was operated on a two-month pilot campaign. Twelve samples of 10 assessments each were collected and the defectives were identified. The percent defects in each sample were calculated and averaged. The standard deviation of % defects was estimated. Pilot data yielding an average of 20% defects and variability of 6% defects were plotted in the control chart below.

The workers in the LTS unit developed this control chart template in Microsoft Excel while using the pilot data as the monthly % defect. Additional discussion on construction continuous at the end of this article.

Reading a Control Chart

A control chart gives a pictorial status of the performance of the service delivery process. The shape of the actual monthly data as plotted on the chart may indicate a stable operation or an operation beset by effects of special causes. This is when a new CI project will be indicated. A control chart has three parts: (1) centerline, i.e. the green line in the chart above, (2) upper and lower control limits, and (3) monthly plots of actual results, i.e. monthly percent assessment defects. Three lanes are shown above and below the centerline. Lane A is within one standard deviation above and under the centerline, while Lane B lays between two and one standard deviations from the centerline, and finally, Lane C lays between the third and the second standard deviation.

The pattern or shape of the actual monthly average percent defects signals that a special and unexpected cause is affecting the service process and an investigation initiated. These shapes are:

Shape 1. One point outside Lane C,

Shape 2. Two out of three points in Lane C or beyond,

Shape 3. Four out of five consecutive points in Lane B or beyond and all five points are on the same side of the canter line.

Shape 4. Six points in a row either increasing or decreasing,

Shape 5. Eight consecutive points outside of Lane A with some over and some below the centerline,

Shape 6. Nine points in a row at the same side of the centerline,

Shape 7. Fourteen points alternatively up and down, and

Shape 8. Fifteen consecutive points in Lane A straddling the centerline.

The Chart Template

A free Excel worksheet with the data entry template and the printable control chart, shown above, is available upon request at contact@mgmtlaboratory.com.

Two yellow cells on top of the template are places for the average defects and standard deviation. These process parameters are determined during pilot operations and stay constant until reset with parameters another improvement project. The third yellowed area receives the monthly actual average percent defects. The centerline, CL is equal to the average % defects. The lower control lines LCL, L2S, and L1S are three, two, and one standard deviation from the centerline. These calculations apply inversely to UCL, U2S, and U1S upper control lines.

By Mgmtlaboratory.com staff 2021.

Mgmtlaboratory.com staff are experienced in the continuous improvement methods in private and public service organizations. Included is the use of graphical and data analysis tools. Government and non-profit entities may inquire at contact@mgmtlaboratory.com about its free online consulting service on continuous improvement.