*
Transforming to Achieve Linearity (C10
BVD)
* Answer: Straighten it!
* Or: Use a curved regression model like
QuadReg, PwrReg
* If not specified, choose to Straighten.
*
* If shape is: levels off Try: square the y-list
* If shape is: possibly half a parabola or a parabola Try:
square root the y-list
* If shape is: all positive y’s, curved Try: take log of y’s (or
ln)
* Others to try: -1/sqrt(y), -1/y, log x, log x and log y
* These are listed roughly in order of “power”:
* If a re-expression bends the curve more, go the other
way, if it bends it too far the other direction, go back up
the list.
* Some version of log re-expression often works.
* It can take a few (or several) tries to find a good
“straightener”. As you gain experience, you will become
faster.
*
* Once straightened, you can do LinReg and do
all the analysis as before, but when you write
the equation, remember your re-expression.
* For example, if your y-list became log(y), then
your equation is log(y)-hat = mx+b
* When using the equation, you may have to
“undo” a log, etc. to get actual predicted y’s.
*