sensspec {longROC}

Sensitivity and Specificity

Description

Compute sensitivity and specificity

Usage

sensspec(X,etime,status,u=NULL,tt,s,vtimes,cutoff=0,fc=NULL)

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

Upper limit (time-horizon) 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

cutoff

cutoff for definining events. Defaults to 0

fc

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

Details

Sensitivity and specificities for a time-dependent multiply-measured marker are defined as

Se(t,c,s,u) = Pr(f_c(X(t_1),X(t_2),...,X(t_s_i))| u <= T <= t),

and

Sp(t,c,s,u) = 1-Pr(f_c(X(t_1),X(t_2),...,X(t_s_i)) | T > t)

for some fixed f_c, where c is a cutoff. The default for f_c is that a positive diagnosis is given as soon as any measurement among the s considered is above the threshold.

Value

A vector with the following elements:

sens	Sensitivity at the cutoff
spec	Specificity at the cutoff

Author(s)

Alessio Farcomeni [e-mail]

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, auc, butstrap, maxauc