[R] anova error

[Jean.Coursol at math.u-psud.fr]

Just for fun

This small program gives negative Sum of Sq in anova (with R versions  
2.9.2 and 2.10.0) (linux 32 kernel 2.6.29.6-smp slackware 13.0) :

y = c(3.6, 5.0, 5.0, 4.6, 4.5, 4.3, 4.5, 5.1, 4.5, 4.3)
trans = as.factor(c("NT","NT","NT","NT","NT","T","T","T","T","T"))
lc = lm(y ~ trans)
l1 = lm(y ~ 1)

anova(l1,lc)

# Analysis of Variance Table
#
# Model 1: y ~ 1
# Model 2: y ~ trans
#   Res.Df   RSS Df  Sum of Sq F Pr(>F)
# 1      9 1.744
# 2      8 1.744  1 -2.220e-16           # negative Sum of Sq ????

anova(lc)  # is OK

# 2.9.2 version
# Analysis of Variance Table
#
# Response: y
#           Df    Sum Sq   Mean Sq   F value Pr(>F)
# trans      1 8.214e-32 8.214e-32 3.768e-31      1
# Residuals  8     1.744     0.218

# 2.10.0 version
# Analysis of Variance Table
#
# Response: y
#           Df Sum Sq Mean Sq F value Pr(>F)
# trans      1  0.000   0.000       0      1
# Residuals  8  1.744   0.218