[R] Interesting behavior of lm() with small, problematic data sets

JRG loesljrg at accucom.net
Wed Sep 6 15:22:18 CEST 2017

Indeed (version-specific).

With R 3.4.1 on linux, I get coefficients and residuals that are
numerically exact, F-statistic = NaN, p-value = NA, R-squared = NaN, etc.

All of which is what ought to happen, given that the response variable
(y) is not actually variable.

John R. Gleason

On 09/06/2017 09:10 AM, S Ellison wrote:
>> I think what you're seeing is
>> https://en.wikipedia.org/wiki/Loss_of_significance.
> Almost. 
> All the results in the OP's summary are reflections of finite precision in the analytically exact solution, leading to residuals smaller than the double precision limit. The summary is correctly warning that it's all potentially nonsense, and indeed the only things you can trust are the coefficient values (to within .Machine$double.eps or thereabouts)
> Interestingly, though, my current version of R (3.4.0) gives numerically exact coefficients (c(1,0) and identically zero standard errors.
> So this particular example is apparently version-specific.
> S Ellison
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