The recent public discussion about the effectiveness of hotel quarantine in isolating the COVID-19 virus has highlighted the importance of understanding and setting appropriate Critical to Quality (CTQ) values. For example, whilst an official value for quarantine effectiveness of 99.9% sounds quite good, that equates to a failure rate of 1 in 1000. To put that in context, would you fly with an airline that gave you a 1 in 1000 chance of not reaching your destination safely? Probably not. Since both examples could be life or death experiences, it's a fair comparison. So with quarantine, there is clearly an opportunity for improvement, given the effects of a failure being the recent shutdown of multiple State capitol cities and potential contagious outbreaks.
So how should CTQ values be set? For many processes, the task is not so complex. Do you really need a six sigma process when a lower value would meet customer specifications? Some areas of a business may not be so critical and hence can have lower targets without affecting overall performance, whilst some will be very critical and require careful design and monitoring.
You can save time and money by selectively setting targets in different areas of the value stream without degrading overall performance and customer satisfaction.