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Missing values with lm
3 messages · Jan Hackenberg, Roger Bivand, piero campa
On Wed, 2 Mar 2011, Jan Hackenberg wrote:
Hello I am trying to fit a linear model with lm. I want to decompose spatial-temporal pm10 data into pure spatial component and pure temporal component with an error term. My data consists of 36 points with 480 timesteps. The code i am using is lm.half <- lm(pm10 ~factor(s) +factor(t),data= half) so i expect to get 36 s values and 480 t values. Instead for the first cell and the first timestep the value is missing, the lm result is only 35 s values and 479 t values ( + one intercept coefficient ). Is there a reason behind this and some way to fix it? Second question is how could i skip the intercept value in my computation. is this simple lm.half <- lm(pm10 ~factor(s) +factor(t) -1,data= half) ?? I have found it in the internet, but i fear that then a -1 is taken into account always...
Don't always trust the internet, but yes, use -1 or equivalently + 0, see:
?formula
or for more detail:
Chambers, J. M. and Hastie, T. J. (1992) _Statistical models._
Chapter 2 of _Statistical Models in S_ eds J. M. Chambers and T.
J. Hastie, Wadsworth & Brooks/Cole.
which is the authoritative source for where formula and data.frame objects
came from.
Roger
And also one last question, my R sqaured value is not too high, its only about 0.51. Does this tell me the model makes no sense? I would very like to use this model but i dont know if this number tells me not to use this ;). Have also heard that linear models without intercept have a higher r quared value, perhaps it will fix a little bit of this. Regards Jan [[alternative HTML version deleted]]
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Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: Roger.Bivand at nhh.no
Hi,
Jan also wrote:
"so i expect to get 36 s values and 480 t values. Instead for the first cell and the first timestep the value is missing, the lm result is only 35 s values and 479 t values ( + one intercept coefficient ). Is there a reason behind this and some way to fix it?" Any clue about this? I encountered a similar problem and worked it out by filling the (very small percentage) of NAs with a simple inverse distance interpolation (?gstat::krige). Piero -- View this message in context: http://r-sig-geo.2731867.n2.nabble.com/Missing-values-with-lm-tp6080805p6084753.html Sent from the R-sig-geo mailing list archive at Nabble.com.