st: linear test

[M.Delprato@westminster.ac.uk]

I want to test if an explanatory variable has linear relationship with an
dependent variable. Say, y = a + b1 x1 + b2 x2 + b3 x3 + e, and I want to know
if the relationship between x3 and y is linear. Which test can I use? Thanks in
advance. M
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