longROC (version 1.0)

plotAUC: AUC as a function of time

Description

Compute area under the ROC curve for several values of time horizon

Usage

plotAUC(X,etime,status,u=NULL,tt,s,vtimes,fc=NULL,plot=TRUE)

Arguments

X

n by S matrix of longitudinal score/biomarker for i-th subject at j-th occasion (NA if unmeasured)

etime

n vector with follow-up times

status

n vector with event indicators

u

Lower limit for evaluation of sensitivity and specificity. Defaults to vtimes[s] (see below)

tt

A vector of upper limits (time-horizons) for evaluation of sensitivity and specificity.

s

Scalar number of measurements/visits to use for each subject. s<=S

vtimes

S vector with visit times

fc

Events are defined as fc = 1. Defaults to $I(cup X(t_j)>cutoff)$

plot

Do we plot the AUCs? Defaults to TRUE

Value

A vector with AUCs

Details

Area under the ROC curve is computed for each value of the vector tt. The resulting vector is returned. If plot=TRUE (which is the default) also a plot of tt vs AUC is displayed.

References

Barbati, G. and Farcomeni, A. (2017) Prognostic assessment of repeatedly measured time-dependent biomarkers, with application to dilated cardiomuopathy, Statistical Methods & Applications, in press

See Also

roc, butstrap, auc

Examples

# NOT RUN {
# parameters
n=25
tt=3
Tmax=10
u=1.5
s=2
vtimes=c(0,1,2,5)

# generate data 

ngrid=1000
ts=seq(0,Tmax,length=ngrid)
X2=matrix(rnorm(n*ngrid,0,0.1),n,ngrid)
for(i in 1:n) {
sa=sample(ngrid/6,1)
vals=sample(3,1)-1
X2[i,1:sa[1]]=vals[1]+X2[i,1:sa[1]]
X2[i,(sa[1]+1):ngrid]=vals[1]+sample(c(-2,2),1)+X2[i,(sa[1]+1):ngrid]
}

S1=matrix(sample(4,n,replace=TRUE),n,length(vtimes))
S2=matrix(NA,n,length(vtimes))

S2[,1]=X2[,1]

for(j in 2:length(vtimes)) {
tm=which.min(abs(ts-vtimes[j]))
S2[,j]=X2[,tm]}

cens=runif(n)
ripart=1-exp(-0.01*apply(exp(X2),1,cumsum)*ts/1:ngrid)

Ti=rep(NA,n)
for(i in 1:n) {
Ti[i]=ts[which.min(abs(ripart[,i]-cens[i]))]
}

cens=runif(n,0,Tmax*2)
delta=ifelse(cens>Ti,1,0)
Ti[cens<Ti]=cens[cens<Ti]

## 

## an important marker 

aucs=plotAUC(S2,Ti,delta,u,seq(2,5,length=5),s,vtimes) 
# }