The drug difference of ex125 (estimate -5.56, variance 0.478, F on 1 and 5 df) and the joint test
that the four cell means are equal: F = 31.2 on 3 and 7.14 df, p = 0.0002.
References
Duchateau, L., Janssen, P. and Rowlands, G. J. (1998). Linear Mixed Models. An Introduction with Applications in Veterinary Research. International Livestock Research Institute, Nairobi.
See also
Other VetResearchLMM examples:
Examp1.3.2,
Examp2.2.1.7,
Examp2.3.2,
Examp2.4.2.2,
Examp2.4.3.1,
Examp2.5.1.1,
Examp2.5.2.1,
Examp2.5.3.1,
Examp2.5.4.1,
Examp3.1,
Examp3.2,
Examp3.3
Author
Muhammad Yaseen (myaseen208@gmail.com)
Examples
# SAS program of the book (Appendix B):
# proc mixed data=ex125;
# class drug dose region;
# model pcv = drug dose drug*dose / ddfm=satterth;
# random region drug*region;
# contrast 'drug dif' drug -1 1 drug*dose -0.5 -0.5 0.5 0.5;
# contrast 'all' drug 1 -1 dose 0 0 drug*dose 0.5 0.5 -0.5 -0.5,
# drug 0 0 dose 1 -1 drug*dose 0.5 -0.5 0.5 -0.5,
# drug 0 0 dose 0 0 drug*dose 0.5 -0.5 -0.5 0.5;
# run;
fm <-
vlm_fit(
fixed = Pcv ~ Drug + dose + Drug:dose
, data = ex125
, random = ~ Region + Region:Drug
, repeated = NULL
, method = "REML"
, ddfm = "satterth"
, type = 3
, class = NULL
, bound = TRUE
, control = list()
)
vlm_contrast(
fit = fm
, L = list(
"drug dif" = list(Drug = c(-1, 1), "Drug:dose" = c(-0.5, -0.5, 0.5, 0.5))
, "all" = list(
list(Drug = c(1, -1), "Drug:dose" = c(0.5, 0.5, -0.5, -0.5))
, list(dose = c(1, -1), "Drug:dose" = c(0.5, -0.5, 0.5, -0.5))
, list("Drug:dose" = c(0.5, -0.5, -0.5, 0.5))
)
)
)
#> Contrasts (denominator df: satterth)
#>
#> Contrasts
#> label num_df den_df F p
#> drug dif 1 5.000 64.58 0.000483
#> all 3 7.143 31.20 0.000179
#>
#> Sources: Duchateau, Janssen and Rowlands (1998); McLean, Sanders and Stroup
#> (1991); Satterthwaite (1946); Giesbrecht and Burns (1985); Fai and Cornelius
#> (1996). Full references: vlm_cite(x).