RE: Prediction

["John K. Balor" <balor1999@yahoo.com>]

Steve Prevette says: "In terms of data, I use SPC to help with the prediction. Yes, SPC on
residuals of a regression should also work, though you run into problems
in predicting within the data used to perform the regression.
Predictions toward the center of the data have a smaller prediction
interval than those extrapolated away from the data. So we can run into
some conceptual problems there."
 
I don't quite understand.  One of the things I do is to monitoring the level of defects, and using regression for estimating the level for the next year.  To check whether the prediction method is statistically stabil, I use SPC.  Do you mean it would be more efficient to plot annual differences and use SPC directly?  What if the regression seems to be exponential rather than linear?
 
John Balor