BTabilities {BradleyTerry2} | R Documentation |
Computes the (baseline) ability of each player from a model object of
class "BTm"
.
BTabilities(model)
model |
a model object for which |
A two-column numeric matrix (of class c("BTabilities", "matrix")
, with columns named "ability"
and "se"
; has
one row for each player; has attributes named "vcov"
,
"modelcall"
, "factorname"
and (sometimes — see below)
"separate"
. The first three attributes are not printed
by the method print.BTabilities
.
The player abilities are either directly estimated by the model, in
which case the appropriate parameter estimates are returned, otherwise
the abilities are computed from the terms of the fitted model that
involve player covariates only (those indexed by model$id
in the model
formula). Thus parameters in any other terms are assumed to be zero.
If the abilities are structured according to a linear predictor, and
if there are player covariates with missing values, the
abilities for the corresponding players are estimated as separate
parameters. In this event the resultant matrix has an attribute, named
"separate"
, which identifies those players whose ability was
estimated separately. For an example, see flatlizards
.
David Firth and Heather Turner
Firth, D. (2005) Bradley-Terry models in R. Journal of Statistical Software, 12(1), 1–12.
Turner, H. and Firth, D. (2012) Bradley-Terry models in R: The BradleyTerry2 package. Journal of Statistical Software, 48(9), 1–21.
### citations example ## Convert frequencies to success/failure data citations.sf <- countsToBinomial(citations) names(citations.sf)[1:2] <- c("journal1", "journal2") ## Fit the "standard" Bradley-Terry model citeModel <- BTm(cbind(win1, win2), journal1, journal2, data = citations.sf) BTabilities(citeModel) ### baseball example baseball$home.team <- data.frame(team = baseball$home.team, at.home = 1) baseball$away.team <- data.frame(team = baseball$away.team, at.home = 0) baseballModel2 <- BTm(cbind(home.wins, away.wins), home.team, away.team, formula = ~ team + at.home, id = "team", data = baseball) ## Estimated abilities for each team, relative to Baltimore, when ## playing away from home: BTabilities(baseballModel2)