A process capability specification is to be customer driven; however, not all processes have true customer derived specifications. These processes are difficult to report a capability value.
The easiest method to report the capability of a process without a true specification is to just report what the range of typical values. In an Integrated Enterprise Excellence (IEE) Business Management System 30,000-foot-level metric report-outs a median value is the most common output followed by a 80% range of occurrence (+/-40% from median). Why 80%, no real reason I guess, it could have been a 90% or 95% range just as easily. We believe that an 80% range of occurrence is close to what a person may view as common.
Non Specification Process Capability Specification with Goal Criteria
Process Goal
A goal is usually considered as the target for the process output. In most cases you want the process average to be equal to the goal. In these cases you can report capability as an average deviation from the specified goal along with an 80% range of common values
Performance Time goal
This type of target is seen often in Service Level Agreements (SLA) where there is an agreement to not exceed the target more than X% of the time. An example would be a call center that agrees to answer at least 95% of all calls within 5 minutes. Reporting performance to this type of goal has two common methods. One method involves reporting the actual percentage above the target time and comparing to 5%. The second method is to count the days that the SLA is met. These two method consider a continuous measure and then convert it to an attribute before reporting. Both of these methods are preferred by management because they track compliance with a commitment to a customer.
As a rule, I would avoid converting continuous data into an attribute for reporting. In this case you are better served by tracking the actual time measurements. Using each point or a average/std.deviation value for sequential periods would provide you better estimate of the process consistency, then you can use a probability plot to report the estimated long term percentage over the SLA value. If you have a stable process, there is no value in reporting the daily SLA agreement, because you know it will vary randomly and you may trigger firefighting activities due to a randomly high value.
In-process upper/lower specification (not customer derived process capability specification)
This might be the most dangerous condition to deal with due to its impact on the entire corporate quality system. In this case you would have a specification value set for an intermediate process characteristic that is not a final customer requirement. It may be a concentration, a weight, a dimension, or almost anything that you use for process control but not for quality control. The business labels it as a specification, but does not scrap product that exceeds the values. You may rework or touch up, but the product or transaction is still processed.
I consider these values not as specifications but as process limits. The term specification should only be used for customer or contract controlled limits that define good and bad. Shipping a product or providing a service that is knowingly bad is just not done. If you label the in-process characteristic limits as process specifications, you have set up a condition where you may excuse the product or service that exceeded the process specification and keep processing it. This just created a dilemma for the workforce. You allow a product or service to continue when it exceeded a specification value at this process, so why not consider that behavior for all specifications. This is why the work specification should only be used for customer or contract based limits that define good and bad. Use action limits or process limits or some other euphemism that the workforce understands that the process may exceed and we will still continue processing with additional consideration.
In these cases, you should report the percent of the product or service that is non-conforming to the process limit. along with assessing the stability of the process.
Process characteristic that has no specified limit or target
These cases are fairly easy. If there is no target or process limits available, then the goal is to keep the output consistent. Report the mean performance and the 80% range of output as long as the process is stable.
Performance without stability.
I can not write about performance reporting without reinforcing the requirement to assess the stability of a process before reporting the performance or capability. Only use data from the most recent period of stability in all performance reporting. If a process is unstable, do not report the capability.
Integrated Enterprise Excellence (IEE) Business Management System for Addressing Process Capability Specification that is a Customer Driven or a Goal
The IEE business management system addresses the business scorecard issues (customer driven specifications or not) that are described in the one-minute video:
IEE is described in the following article:
The IEE system is described in a 5-book series:
Contact Us to set up a time to discuss with Forrest Breyfogle how your organization might gain much from an Integrated Enterprise Excellence (IEE) Business Process Management System and its process capability specification (customer driven or goal setting) reporting.