Shift Schedules and Six Sigma

Both Lean, and Six Sigma methods can be used to minimize waste and improve efficiency in business operations. In our blog post “Is your Shift Schedule Lean?” we addressed potential waste sources in shift schedules. This is a Lean approach to evaluating a shift schedule.

What about Six Sigma and Shift Schedules?

While Lean’s focus is on eliminating waste in the overall process under consideration, Six Sigma looks at minimizing variability in the process using a data-driven evaluation process. Root causes are identified and verified by actual data. Six Sigma methods can be mathematical, but they are very powerful too.

We can use Six Sigma methods to answer questions like: Is the shift schedule causing productivity to vary in our operation?

A common belief in shiftwork operations is that a particular shift (often believed to be night shift) has lower performance than the other shifts. Similarly, shift workers working on a particular day of the week (weekend days are a common target) may be believed to have lower performance. Or, perhaps the first shift worked after a long break is believed to be a low-performance day. Six Sigma methods can help us test those beliefs and separate the normal operating variability from real, shift-schedule, related problems.

Let’s look at an example of using Six Sigma methods to evaluate a shiftwork operation. Several years ago, Shiftwork Solutions worked with a consumer products company considering a schedule change from 24×5 (Monday-Friday, 8-hour shifts) to a 24×7 schedule. The average daily production volume, by shift, is shown in the table below:

Average production levels of a three shift operation over a six month period.
Daily average production levels on each shift over a six-month period.

It doesn’t take a Six Sigma Blackbelt to conclude that the third shift is producing less than the other two shifts. Total production is a performance measure, but without knowing the actual labor hours (or some other similar measure of effort invested), it is difficult to draw any conclusions beyond the obvious difference between shifts in the average production/shift.

Taking into account the direct labor hours used, the same production performance looks like this:

Average productivity levels of a three shift operation over a six month period.
Daily average productivity levels on each shift over a six-month period.

Now what? We see differences between the shifts, but we can’t tell if they are real differences or just a reflection of the noise in the system. The second shift is clearly more productive than the other two shifts.
As Donald Wheeler says (on page 30 of Understanding Variation): “While every data set contains noise, some data sets contain signals. Therefore, before you can detect a signal within a given data set, you must first filter out the noise.” Do we have noise here, or should we be evaluating how we are managing our shift work operations?

First, let’s look at the total production levels between shifts. We know that 3rd shift is clearly lower, but is the first shift performance actually lower than the second shift? If we perform an analysis of variance (ANOVA) between the 1st and 2nd shifts, we find that the answer, with a 5% significance level (the risk that our hypothesis is false, even though it appears to be true using ANOVA), is yes (F > Fcrit). Here’s the ANOVA table:

ANOVA table comparing the first shift to the second shift.  F is greater than Fcrit.
Analysis of variance (ANOVA) of the first and second shift daily production levels at a 5% significance level.

What about the difference in productivity? Is the first shift more productive than the third shift? Performing an ANOVA analysis on that data yields:

ANOVA table comparing the first shift productivity to the third shift productivity.  F is less than Fcrit.
Analysis of variance (ANOVA) of the first and third shift daily productivity levels at a 5% significance level.

In this case, F<Fcrit, and we cannot conclude that there is a difference in performance between the first and third shifts at the 5% significance level.

What does all this tell us? The second shift is much more productive than the first and third shifts. The first and third shifts, statistically, are equally productive.
Questions that we need to investigate:

  1. Why is the second shift more productive than the first and third shifts?
  2. What explains the difference in overall production levels, given the productivity levels?
  3. Is it the shift schedule a contributing factor?
  4. How do we get the first and third shift up to the second shift’s productivity level?

Finally, back to our original question about the shift schedule: Is the shift schedule causing productivity to vary in our operation? At this point, we don’t know if it is the shift schedule, but we cannot rule it out. We have more work to do.

We can help you evaluate your shift work operations and help you solve the actual problems that are limiting your operational performance.

Call us today at (435) 200-5566.

Is Your Shift Schedule Lean?

There are many aspects to the concept of Lean Manufacturing and Lean Thinking.  One of the fundamental goals of applying lean concepts is to eliminate waste in the process. 

What can we do to minimize waste in shift schedules?  In no specific order, here are some places to look:

  1. Match the coverage to the workload
    • A headcount mismatch creates idle time, overtime, and lost capacity (if you are unable to run)
    • Avoid overstaffing to cover absences.
  2. Create time for preventative maintenance
    • Make your product right the first time – avoid defects and extra processing resulting from machines that are out of adjustment.
    • Avoid waiting due to breakdowns.
    • Reduce operating costs due to improved equipment efficiency.
  3.  Allow shift workers to get rest (days off, hours/day)
    • Reduce defects due to human error.
    • Feel better, better performance, clearer thinking, and more interest in engagement.
    • Less pacing due to fatigue.
  4. Smooth production and create flow using a continuous schedule (24×7)
    • Reduce finished goods and work-in-process inventory.
    • Match production to demand.
    • Find defects when they occur and correct the cause immediately.
    • Maximize asset utilization.
    • One potential risk is the increase in overhead staff because of an increase in the number of supervisors and indirect support personnel.
  5. Operate through breaks and lunches
    • Avoid line instability that results in defects and line startup/shutdown costs.
    • Maximize capacity and asset utilization.
  6. Insufficient cross-training
    • Waiting to get the right person for the job
    • Not utilizing the potential for on-shift personnel to fill more roles

I’m sure you can come up with more opportunities to add to my list.   

Improving your schedule by addressing sources of waste requires making changes.  Changing schedules is not easy, but it can be done.  Our change process engages the workforce in the schedule evaluation and incorporates their feedback into the best solutions that result in a leaner, more efficient, and productive operation.

Call us today at (435) 200-5566 to discuss your operations and how we can help you solve your shift work problems. You can also complete our contact form and we will call you.