These correlations between outcome and input are generally accomplished through well-established statistical methods such as linear regression. Where on-line SPC focuses on ensuring critical limits are maintained and that significant trends are recognized and addressed, SQC offers the capability of discovering new critical limits and new factors affecting quality. Charts and reports have to able to convince managers to take needed action and to convince customers that you are in control. If they don't help you do this, you are at a real disadvantage. A lot of the problems people encounter in implementing SPC stem from the fact that SPC is initially implemented out of an almost mindless imperative.
Implementation is done without determination.
People load up software and start printing charts, and then they wonder why there aren't tangible results. Manufacturing is evolving away from inspection. SPC implementation can involve significant internal costs and effort, and in a company culture where everyone is encouraged to concern themselves with quality, there is likely to be greater management support for the implementation of SPC in the face of these costs, and less likely for there to be inter-departmental squabbling over the temporary inconveniences of implementation. It may be because of the culture of the industry where you are dealing with a lot of old, established companies. It's hard to say.