# How do I satisfy the nonlinearity of my regression function with this plot image?

I have some problem with the transformation of my data. This is my project in my regression class, and we're asked to run our data and satisfy all the possible assumptions, until we can chose a model. Which we're going to use for prediction. Now, I tried all possible transformations, but It doesn't give me any solution to make this scatter plot linear. Or is there any test that I can use to check the linearity of my data? Than using informal method of looking to the plot only.

Well, Here's the plot image of Residual versus the Fitted Values.

I tried log-transforming, modifying my regression function, and etc. But still it doesn't make linear.

Though, I check the constancy of my error variance using the Breusch-Pagan test, which concludes it to be constant.

But, I don't know any other test for checking Non-linearity.

• Hi there and welcome to the site. You look like you might have hetereoscedasticity in your residuals - the residuals appear to be getting larger with increasing fitted values. I assume your fitted values are the logs, have you tried a stronger transform, e.g. as suggested by boxcox() from the MASS package, as suggested by @StéphaneLaurent above? – Michelle Mar 18 '12 at 9:40