For the 34 sheep sires, the number of lambs in each of 5 foot shape classes.

Usage

data("alwan.lamb")

Format

A data frame with 340 observations on the following 11 variables.

year: numeric 1980/1981
breed: breed PP, BRP, BR
sex: sex of lamb M/F
sire0: sire ID according to Alwan
shape: sire ID according to Gilmour
count: number of lambs
sire: shape of foot
yr: numeric contrast for year
b1: numeric contrast for breeds
b2: numeric contrast for breeds
b3: numeric contrast for breeds

Details

There were 2513 lambs classified on the presence of deformities in their feet. The lambs represent the offspring of 34 sires, 5 strains, 2 years.

The variables yr, b1, b2, b3 are numeric contrasts for the fixed effects as defined in the paper by Gilmour (1987) and used in the SAS example. Gilmour does not explain the reason for the particular contrasts. The counts for classes LF1, LF2, LF3 were combined.

Source

Mohammed Alwan (1983). Studies of the flock mating performance of Booroola merino crossbred ram lambs, and the foot conditions in Booroola merino crossbreds and Perendale sheep grazed on hill country. Thesis, Massey University. https://hdl.handle.net/10179/5900 Appendix I, II.

References

Gilmour, Anderson, and Rae (1987). Variance components on an underlying scale for ordered multiple threshold categorical data using a generalized linear mixed model. Journal of Animal Breeding and Genetics, 104, 149-155. https://doi.org/10.1111/j.1439-0388.1987.tb00117.x

SAS/STAT(R) 9.2 Users Guide, Second Edition Example 38.11 Maximum Likelihood in Proportional Odds Model with Random Effects https://support.sas.com/documentation/cdl/en/statug/63033/HTML/default/viewer.htm

Examples

if (FALSE) { # \dontrun{

  library(agridat)
  data(alwan.lamb)
  dat <- alwan.lamb

  # merge LF1 LF2 LF3 class counts, and combine M/F
  dat$shape <- as.character(dat$shape)
  dat$shape <- ifelse(dat$shape=="LF2", "LF3", dat$shape)
  dat$shape <- ifelse(dat$shape=="LF1", "LF3", dat$shape)
  dat <- aggregate(count ~ year+breed+sire0+sire+shape+yr+b1+b2+b3,
                   dat, FUN=sum)

  dat <- transform(dat,
                   year=factor(year), breed=factor(breed),
                   sire0=factor(sire0), sire=factor(sire))
  # LF5 or LF3 first is a bit arbitary...affects the sign of the coefficients
  dat <- transform(dat, shape=ordered(shape, levels=c("LF5","LF4","LF3")))
  
  # View counts by year and breed
  libs(latticeExtra)
  dat2 <- aggregate(count ~ year+breed+shape, dat, FUN=sum)
  useOuterStrips(barchart(count ~ shape|year*breed, data=dat2,
                          main="alwan.lamb"))

  # Model used by Gilmour and SAS
  dat <- subset(dat, count > 0) 
  libs(ordinal)
  m1 <- clmm(shape ~ yr + b1 + b2 + b3 + (1|sire), data=dat,
             weights=count, link="probit", Hess=TRUE)
  summary(m1) # Very similar to Gilmour results
  ordinal::ranef(m1) # sign is opposite of SAS

  ## SAS var of sires .04849
  ## Effect   Shape   Estimate   Standard Error   DF   t Value   Pr > |t|
  ## Intercept   1   0.3781   0.04907   29   7.71   <.0001
  ## Intercept   2   1.6435   0.05930   29   27.72   <.0001
  ## yr       0.1422   0.04834   2478   2.94   0.0033
  ## b1       0.3781   0.07154   2478   5.28   <.0001
  ## b2       0.3157   0.09709   2478   3.25   0.0012
  ## b3       -0.09887   0.06508   2478   -1.52   0.1289
  
  ## Gilmour results for probit analysis
  ## Int1   .370 +/- .052
  ## Int2  1.603 +/- .061
  ## Year  -.139 +/- .052
  ## B1    -.370 +/- .076
  ## B2    -.304 +/- .103
  ## B3     .098 +/- .070

  # Plot random sire effects with intervals, similar to SAS example
  plot.random <- function(model, random.effect, ylim=NULL, xlab="", main="") {
    tab <- ordinal::ranef(model)[[random.effect]]
    tab <- data.frame(lab=rownames(tab), est=tab$"(Intercept)")
    tab <- transform(tab,
                     lo = est - 1.96 * sqrt(model$condVar),
                     hi = est + 1.96 * sqrt(model$condVar))
    # sort by est, and return index
    ix <- order(tab$est)
    tab <- tab[ix,]
    
    if(is.null(ylim)) ylim <- range(c(tab$lo, tab$hi))
    n <- nrow(tab)
    plot(1:n, tab$est, axes=FALSE, ylim=ylim, xlab=xlab,
         ylab="effect", main=main, type="n")
    text(1:n, tab$est, labels=substring(tab$lab,2) , cex=.75)
    axis(1)
    axis(2)
    segments(1:n, tab$lo, 1:n, tab$hi, col="gray30")
    abline(h=c(-.5, -.25, 0, .25, .5), col="gray")
    return(ix)  
  }
  ix <- plot.random(m1, "sire")

  # foot-shape proportions for each sire, sorted by estimated sire effects
  # positive sire effects tend to have lower proportion of lambs in LF4 and LF5
  tab <- prop.table(xtabs(count ~ sire+shape, dat), margin=1)
  tab <- tab[ix,]
  tab <- tab[nrow(tab):1,] # reverse the order
  lattice::barchart(tab,
                    horizontal=FALSE, auto.key=TRUE,
                    main="alwan.lamb", xlab="Sire", ylab="Proportion of lambs",
                    scales=list(x=list(rot=70)),
                    par.settings = simpleTheme(col=c("yellow","orange","red")) )
  
  detach("package:ordinal") # to avoid VarCorr clash with lme4
  
} # }