Hi!
I try to explain the efffect of (1) forest where i took samples's soils (*
Lugar*: categorical variable with three levels), (2) nitrogen addition
treatments (*Tra*: categorical variable with two levels) on total carbon
concentration's soil samples (*C: *continue* *variable) during four months
of sampling (*Time:* categorical and ordered variable with four levels).
I fitted the following final model with gls function:
var1<-varIdent(form=~ 1| Lugar* factor(Time))
FINAL<-gls(C ~ Tra+ Lugar+ Time + Time*Tra + Tra*Lugar, data=datos,
weights=var1, method="REML")
the summary function resulted in this first data's set (I omit correlation's
matrix):
Generalized least squares fit by REML
Model: C ~ Tra + Lugar + Time + Time * Tra + Tra * Lugar
Data: datos
AIC BIC logLik
1129.458 1191.982 -540.7291
Variance function:
Structure: Different standard deviations per stratum
Formula: ~1 | Lugar * factor(Time)
Parameter estimates:
Chixchulub*0 Xmatkuil*0 Hobonil*0 Chixchulub*2 Xmatkuil*2
Hobonil*2 Chixchulub*3
1.0000000 0.7759324 0.5300811 0.9640559 0.8200742
0.2966545 0.9553168
Xmatkuil*3 Hobonil*3 Chixchulub*4 Xmatkuil*4 Hobonil*4
1.7350290 0.3430286 0.6241658 0.9573922 0.4651515
Coefficients:
Value Std.Error t-value
p-value
(Intercept) 260.48540 16.48991 15.796653 0.0000
Tra0 -9.38703 23.74893 -0.395261 0.6935
LugarChixchulub -0.15377 19.60260 -0.007845 0.9938
Lugar Hobonil -173.21354 15.89736 -10.895741 0.0000
Time2 -14.74999 14.55909 -1.013112 0.3135
Time3 14.42177 15.64594 0.921758 0.3589
Time4 14.77803 16.72367 0.883659 0.3790
Tra0:Time2 17.93859 20.78257 0.863156 0.3901
Tra0:Time3 -48.77118 22.17628 -2.199250 0.0302
Tra0:Time4 -52.63611 23.20192 -2.268610 0.0254
Tra0:LugarChixchulub 74.43956 28.11275 2.647893 0.0094
Tra0:Lugar Hobonil 43.03416 23.32391 1.845066 0.0680
anova function generated this table:
enom. DF: 100
numDF F-value p-value
(Intercept) 1 1693.1234 <.0001
Tra 1 5.3225 0.0231
Lugar 2 247.7047 <.0001
Time 3 0.4767 0.6992
Tra:Time 3 6.0531 0.0008
Tra:Lugar 2 3.5061 0.0338
I want to detetect differences between levels of Tra:Lugar interaction. For
example:
1. Tra0:LugarChixchulub vs Tra1:LugarChixchulub (between treatment levels
for same forest) or,
2. Tra0:LugarChixchulub vs Tra0:LugarHobonil (for same treatment
among forests levels)
I used function contrast (package contrast) whit following script to probe
the hypotesis 1.:
con<-contrast(FINAL, list(Lugar= 'Xmatkuil', Tra=1), list(Lugar='Xmatkuil',
Tra = 0))
but i found this error message:
Error en gendata.default(fit = list(modelStruct = list(varStruct =
c(-0.253689933940456, :
not enough factors
I would be grateful if somebody tell me I'm doing wrong with my contrast
function script.
Thanks in advance,
Marylin Bejarano
PHd candidate in Ecology Institute of Mexico's National Autonomous
University
[[alternative HTML version deleted]]
______________________________________________
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
