The Math Forum

Search All of the Math Forum:

Views expressed in these public forums are not endorsed by NCTM or The Math Forum.

Math Forum » Discussions » Courses » ap-stat

Notice: We are no longer accepting new posts, but the forums will continue to be readable.

Topic: More on nonlinear models
Replies: 2   Last Post: Oct 31, 1996 6:16 PM

Advanced Search

Back to Topic List Back to Topic List Jump to Tree View Jump to Tree View   Messages: [ Previous | Next ]
James Lang

Posts: 48
Registered: 12/6/04
More on nonlinear models
Posted: Oct 30, 1996 1:22 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply

One comment that Dick Scheaffer made was

>It should be pointed out to students that fitting a least squares line
>to the transformed data is not the same as fitting a nonlinear
>model directly by least squares.

If you would like an example, I have some data on Toyota Corolla prices
that I got from the Orlando Sentinel classified ads. The variables are the
age of the car and the advertised price.

Age Price
1 11500
1 12000
3 8000
5 6000
6 3500
6 3000
6 4500
6 4000
8 4000
9 2200
10 3000
12 1000
12 600
16 600

If you do a ExpReg you get y = 14837.73(0.80851^x) which has SSE = 6431130.

Using a couple data points, (1,11500) and (16,600), that appeared to be a
good visual fit to estimate a,b
I got y = 14002.35(0.82129^x) which has SSE = 6302004.

The point is that the visual fit gave a smaller SSE than the regression on
the transformed data. There is nothing special about this data. You can do
this with any data set that "appears" to be exponential but has some
deviation from the exponential model.

James Lang
Valencia Community College
Orlando, FL

Point your RSS reader here for a feed of the latest messages in this topic.

[Privacy Policy] [Terms of Use]

© The Math Forum at NCTM 1994-2018. All Rights Reserved.