# Error evalution for linear fits

I have some data that looks almost linear. I need to make a fit in order to evaluate the slope. The thing is, the slope is changing if I change the fit range (not all the data is linear so I need to choose myself the range) I wondered how would you suggest to evaluate the added error from the arbitrary selection of the range. For example, maybe I should make a few fits for a few ranges, and take the "range of slopes"/stdv as the added uncertainty?
thanks

• Hi, welcome to OR.SE. Could you provide an example to illustrate the mentioned behavior? So that the question is understood more clearly. – dhasson Jun 15 '20 at 18:03
• Are you required to come up with a linear fit (single constant slope), or can you do a piecewise-linear fit as Kevin Dalmeijer suggests? Also, are there just two variables (the one you are predicting and a single explanatory variable) or is it multidimensional? – prubin Jun 15 '20 at 19:10