Description Usage Arguments Details Value Note Author(s) References Examples
This function finds the posterior mode of the log-linear parameters of a log-linear model with a given design matrix and prior distribution.
1 | beta_mode(X, prior = "SBH", y, IP , a = 0.001 , b = 0.001)
|
X |
The n by p design matrix where n is the number of cells and p is the number of log-linear parameters. |
prior |
The prior distribution. It can be one of |
y |
The n by 1 vector of cell counts. |
IP |
A p by p matrix giving the inverse of the prior scale matrix. |
a |
The shape hyperparameter of the Sabanes-Bove & Held prior, see Overstall & King (2014). |
b |
The scale hyperparameter of the Sabanes-Bove & Held prior, see Overstall & King (2014). |
The posterior mode is found by maximising the log unnormalised posterior pdf given by the sum of the log-likelihood and the log of the prior pdf. This optimisation is achieved using a quasi Newton-Raphson method.
For details on the unit information and Sabanes-Bove & Held priors for generalised linear models see Ntzoufras et al (2003) and Sabanes-Bove & Held (2011), respectively. See Overstall & King (2014), and the references therein, for their application to log-linear models and contingency tables.
The posterior mode is required for the reversible jump algorithm implemented from Forster et al (2012).
beta_mode
will return a p by 1 vector containing the posterior mode of the log
linear parameters.
This function will not typically be called by the user.
Antony M. Overstall A.M.Overstall@soton.ac.uk.
Sabanes-Bove, D. & Held, L. (2011) Hyper-g priors for generalized linear models. Bayesian Analysis, 6 (3), 387–410.
Forster, J.J., Gill, R.C. & Overstall, A.M. (2012) Reversible jump methods for generalised linear models and generalised linear mixed models. Statistics and Computing, 22 (1), 107–120.
Nztoufras, I., Dellaportas, P. & Forster, J.J. (2003) Bayesian variable and link determination for generalised linear models. Journal of Statistical Planning and Inference, 111 (1), 165–180.
Overstall, A.M. & King, R. (2014) conting: An R package for Bayesian analysis of complete and incomplete contingency tables. Journal of Statistical Software, 58 (7), 1–27. http://www.jstatsoft.org/v58/i07/
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 | data(AOH) ## loads the AOH data
X<-model.matrix(~alc+hyp+obe,data=AOH,
contrasts=list(alc="contr.sum",hyp="contr.sum",obe="contr.sum"))
## Sets up the design matrix for the independence model
IP<-(t(X)%*%X)/dim(X)[1]
## Set up inverse of prior scale matrix
beta_mode(X=X,prior="UIP",y=AOH$y,IP=IP)
## Finds the posterior mode of the log-linear parameters under the
## independence model with the unit information prior. Will get:
#X(Intercept) Xalc1 Xalc2 Xalc3 Xhyp1 Xobe1
# 2.894270420 -0.045859743 -0.071775824 0.089541068 -0.504141954 0.008163604
# Xobe2
#-0.016327209
beta_mode(X=X,prior="SBH",y=AOH$y,IP=IP)
## Finds the posterior mode of the log-linear parameters under the
## independence model with the Sabanes-Bove & Held prior. Will get:
#X(Intercept) Xalc1 Xalc2 Xalc3 Xhyp1 Xobe1
# 2.908298763 -0.043704371 -0.068212247 0.085338704 -0.473628107 0.007762839
# Xobe2
#-0.015525678
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