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pattern, i.e., an unexpected snow storm in Atlanta will reduce daily output of a
precast work team. One way to differentiate special versus common cause is to
ask if this is a unique problem or an example of a larger class of problems and
second ask, "If I replace the workers, would I still have this problem?"
The following table gives an example of special versus common cause drivers of
delays in architect’s approvals:
Special Causes Common Causes
• Architect’s wife dies in car accident
• Drawings delivered to wrong office,
where they sat for days
• Architect does not appreciate need
for speedy approval
• Architect is understaffed
• Architect is unfamiliar with precast
and therefore needs to find outside
help prior to approval
• Other parts of design that affect us
are not yet complete
• Approvals are used to help finalize
the drawings
The key to minimizing adverse outcomes from special variation is to ensure you
have a process in place to get timely data that reveals special causes quickly so
that you can react to them. In a hospital setting, for example, highly difficult
cases are flagged early on so that a case manager can help oversee the care of a
patient. The goal is to contain damage with an immediate remedy. It is
important to understand what’s different this time, i.e., what’s causing the special
cause outcome, as this special cause outcome could in fact become a common
cause at some point. If you think it might become a common cause at some
point, then you must develop a longer-term remedy.
How do you deal with special causes?
• Get timely data so that special causes are revealed quickly
• Contain damage with an immediate remedy
• Search for the cause -- what was different? Could it be a common cause at
some point?
• If so, develop a longer-term remedy
The focus of continuous process improvement, and process redesign for that
matter, is to adjust common causes of adverse outcomes. Here you look at all the
data, not a single data point, and you stratify the data into high occurrence causes
and low occurrence causes and you focus initially on improving or limiting the
high occurrence causes. You may ultimately treat different classes of projects
differently if you see correlations between sources of problems and types of
projects.
Pamphlet #5 Page 218