1. Transforming to Achieve Linearity (C10 BVD)
AP Statistics Review
Transforming to Achieve Linearity (C10 BVD)

2. Answer: Straighten it!
Or: Use a curved regression model like QuadReg, PwrReg
If not specified, choose to Straighten.
How do I model the relationship between data if the scatterplot isn’t “straight”?

3. How to Straighten a Curve
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.
How to Straighten a Curve

4. 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.
Writing the Equation