Bivariate Data Pt. 4 October 2011. Gotchas Don’t fit a straight line to a nonlinear relationship. Use residual plots to determine if the linear fit is.

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Presentation transcript:

Bivariate Data Pt. 4 October 2011

Gotchas Don’t fit a straight line to a nonlinear relationship. Use residual plots to determine if the linear fit is acceptable. Beware of extraordinary and unusual points, but never change the data to make it fit. – Errors can be made in data collection, but they should not be “fixed” by the statistician. Don’t extrapolate beyond the data. The assumptions that are in place for a linear model do not necessarily extend beyond the given predictor values.

More gotchas Do not assume that the predictor causes the response just because the linear model is good. Never choose a model based on R 2 alone. Always check the residual plot for additional info.