# [Rd] Possible bug (PR#633)

**Peter Dalgaard BSA
**
p.dalgaard@biostat.ku.dk

*13 Aug 2000 23:59:44 +0200*

agusalon@mcr.ucm.es writes:
>* Rail^0 Rail^1 Rail^2 Rail^3 Rail^4 Rail^5
*>* 66.5 54.303 -4.692 -2.658 -0.567 11.192
*>* which do not seem correct.
*>*
*>* Those reported in the book are:
*>*
*>* Rail2 Rail5 Rail1 Rail6 Rail3 Rail4
*>* 31.667 50 54 82.667 84.667 96
*
This is a matter of differing conventions in handling
lm(travel ~ Rail - 1, data = Rail)
when Rail is an ordered factor. R uses polynomial contrasts in the
no-intercept case as it does when the intercept is present, whereas
Splus treats the ordered factor as if it were an unordered factor. If
you do something like the below, you get your coefficients.
I suspect that this could indeed be argued to be a bug in R, but
others may know better.
>* lm(travel ~ factor(Rail,ordered=F)-1, data = Rail)
*
Call:
lm(formula = travel ~ factor(Rail, ordered = F) - 1, data = Rail)
Coefficients:
factor(Rail, ordered = F)2 factor(Rail, ordered = F)5
31.67 50.00
factor(Rail, ordered = F)1 factor(Rail, ordered = F)6
54.00 82.67
factor(Rail, ordered = F)3 factor(Rail, ordered = F)4
84.67 96.00
--
O__ ---- Peter Dalgaard Blegdamsvej 3
c/ /'_ --- Dept. of Biostatistics 2200 Cph. N
(*) \(*) -- University of Copenhagen Denmark Ph: (+45) 35327918
~~~~~~~~~~ - (p.dalgaard@biostat.ku.dk) FAX: (+45) 35327907
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