uvsdSample: Function uvsdSample

In hbmem: Hierarchical Bayesian Analysis of Recognition Memory

Function uvsdSample

Description

Runs MCMC estimation for the hierarchical UVSD model.

Usage

uvsdSample(dat, M = 10000, keep = (M/10):M, getDIC = TRUE,
freeCrit=TRUE, equalVar=FALSE, freeSig2=FALSE, Hier=TRUE,jump=.0001)

Arguments

dat	Data frame that must include variables Scond,cond,sub,item,lag,resp. Scond indexes studied/new, whereas cond indexes conditions nested within the studied or new conditions. Indexes for Scond,cond, sub, item, and response must start at zero and have no gaps (i.e., no skipped subject numbers). Lags must be zero-centered.
M	Number of MCMC iterations.
keep	Which MCMC iterations should be included in estimates and returned. Use keep to both get ride of burn-in, and thin chains if necessary
getDIC	Logical. should the function compute DIC value? This takes a while if M is large.
freeCrit	Logical. If TRUE (default) individual criteria vary across people. If false, all participants have the same criteria. This should be set to false if there is only one participant, e.g., if averaging data over subjects.
equalVar	Logical. If FALSE (default), unequal-variance model is fit. If TRUE, equal-variance model is fit.
freeSig2	Logical. If FALSE (default), one sigma is fit for all participants and items (as in Pratte, et al., 2009). If TRUE, then an additive model is placed on the log of sigma2 (as in Pratte and Rouder (2010).
Hier	Logical. If TRUE then the variances of effects (e.g., item effects) are estimated from the data, i.e., effects are treated as random. If FALSE then these variances are fixed to 2.0 (.5 for recollection effects), thus treating these effects as fixed. This option is there to allow for compairson with more traditional approaches, and to see the effects of imposing hierarcical structure. It should always be set to TRUE in real analysis, and is not even guaranteed to work if set to false.
jump	The criteria and decorrelating steps utilize Matropolis-Hastings sampling routines, which require tuning. All MCMC functions should self tune during the burnin perior (iterations before keep), and they will alert you to the success of tuning. If acceptance rates are too low, "jump" should be decreased, if they are too hight, "jump" should be increased. Alternatively, or in addition to adjusting "jump", simply increase the burnin period which will allow the function more time to self-tune.

Value

The function returns an internally defined "uvsd" S4 class that includes the following components

mu	Indexes which element of blocks contain grand means, mu
alpha	Indexes which element of blocks contain participant effects, alpha
beta	Indexes which element of blocks contain item effects, beta
s2alpha	Indexes which element of blocks contain variance of participant effects (alpha).
s2beta	Indexes which element of blocks contain variance of item effects (beta).
theta	Indexes which element of blocks contain theta, the slope of the lag effect
estN	Posterior means of block parameters for new-item means
estS	Posterior means of block parameters for studied-item means
estS2	Posterior means of block for studied-item variances.
estCrit	Posterior means of criteria
blockN	Each iteration for each parameter in the new-item mean block. Rows index iteration, columns index parameter.
blockS	Same as blockN, but for the studied-item means
blockS2	Same as blockN, but for variances of studied-item distribution. If equalVar=TRUE, then these values are all zero. If UVSD is fit but freeSig2=FALSE, then only the first element is non-zero (mu).
s.crit	Samples of each criteria.
pD	Number of effective parameters used in DIC. Note that this should be smaller than the actual number of parameters, as constraint from the hierarchical structure decreases the number of effective parameters.
DIC	DIC value. Smaller values indicate better fits. Note that DIC is notably biased toward complexity.
M	Number of MCMC iterations run
keep	MCMC iterations that were used for estimation and returned
b0	Metropolis-Hastings acceptance rates for decorrelating steps. These should be between .2 and .6. If they are not, the M, keep, or jump need to be adjusted.
b0S2	If additive model is placed on Sigma2 (i.e., freeSigma2=TRUE), then all parameters on S2 must be tuned. b0S2 are the acceptance probabilities for these parameters.

Author(s)

Michael S. Pratte

References

See Pratte, Rouder, & Morey (2009)

See Also

hbmem

Examples

#In this example we generate data from UVSD with a different muN,muS,and
#Sigma2 for every person and item. These data are then fit with 
#hierarchical UVSD allowing participant or item effects on log(sigma2).

library(hbmem)
sim=uvsdSim(NN=1,muN=-.5,NS=2,muS=c(.5,1),I=30,J=300,s2aN = .2, s2bN = .2,
muS2=log(c(1.3,1.5)),s2aS=.2,s2bS=.2,s2aS2=.2,s2bS2=.2)
dat=as.data.frame(cbind(sim@subj,sim@item,sim@cond,sim@Scond,sim@lag,sim@resp))
colnames(dat)=c("sub","item","cond","Scond","lag","resp")

M=10 #Way too low for real analysis
keep=2:M
uvsd=uvsdSample(dat,M=M,keep=keep,equalVar=FALSE,freeSig2=TRUE,jump=.0001,Hier=1)

par(mfrow=c(3,2),pch=19,pty='s')
#Look at chains of MuN and MuS
matplot(uvsd@blockN[,uvsd@muN],t='l',xlab="Iteration",ylab="Mu-N")
abline(h=sim@muN,col="blue")
matplot(uvsd@blockS[,uvsd@muS],t='l',xlab="Iteration",ylab="Mu-S")
abline(h=sim@muS,col="blue")

#Estimates of strength effects as function of true values
plot(uvsd@estN[uvsd@alphaN]~sim@alphaN,xlab="True
Alpha-N",ylab="Est. Alpha-N");abline(0,1,col="blue")
plot(uvsd@estS[uvsd@alphaS]~sim@alphaS,xlab="True
Alpha-S",ylab="Est. Alpha-S");abline(0,1,col="blue")
plot(uvsd@estN[uvsd@betaN]~sim@betaN,xlab="True
Beta-N",ylab="Est. Beta-N");abline(0,1,col="blue")
plot(uvsd@estS[uvsd@betaS]~sim@betaS,xlab="True
Beta-S",ylab="Est. Beta-S");abline(0,1,col="blue")

#Sigma^2 effects
#Note that Sigma^2 is biased high with
#few participants and items.  This bias
#goes away with larger sample sizes.
par(mfrow=c(2,2),pch=19,pty='s')
matplot(sqrt(exp(uvsd@blockS2[,uvsd@muS])),t='l',xlab="Iteration",ylab="Mu-Sigma2")
abline(h=sqrt(exp(sim@muS2)),col="blue")
plot(uvsd@blockS2[,uvsd@thetaS],t='l')

plot(uvsd@estS2[uvsd@alphaS]~sim@alphaS2,xlab="True
Alpha-Sigma2",ylab="Est. Alpha-Sigma2");abline(0,1,col="blue")
plot(uvsd@estS2[uvsd@betaS]~sim@betaS2,xlab="True
Beta-Sigma2",ylab="Est. Beta-Sigma2");abline(0,1,col="blue")

#Look at some criteria
par(mfrow=c(2,2))
for(i in 1:4)
matplot(t([e-mail][i,,]),t='l')

hbmem documentation built on Aug. 23, 2023, 1:10 a.m.