Description Usage Arguments Value References Examples
This function estimates the AUC, TPR(c), FPR(c), PPV(c), and NPV(c) for for a specific timepoint and marker cutoff value c with survival data from a case-cohort subcohort design.
1 2 3 4 5 6 7 | survMTP.cch(time, event, marker,
weights,
subcoh,
data,
estimation.method = 'NP',
predict.time,
marker.cutpoint = 'median')
|
time |
time to event |
event |
indicator for the status of event of interest. event = 0 for censored observations, and event = 1 for event of interest. |
marker |
marker variable of interest |
weights |
sample weights from a case-cohort sample design. Should be equal to 1/Pr(sampled from cohort). |
subcoh |
indicator for subjects included in the subcohort sample (1=included, 0=not included) |
data |
data frame in which to look for input variables. This should be the full cohort data, including time, event, weights, subcoh, and marker values when subcoh = 1. |
estimation.method |
should non-parametric ('NP') or semi-parametric ('SP') estimates be calculated. Semi-parametric methods assume a proportional hazards model. |
predict.time |
numeric value of the timepoint of interest for which to estimate the risk measures |
marker.cutpoint |
numeric value indicating the value of the
cutpoint 'c' at which to estimate 'FPR', 'TPR', 'NPV' or
'PPV'. default is |
a list with components
estimates |
point estimates for risk measures |
model.fit |
*only returned if estimation.method = 'SP'* object of type
'coxph' from fitting the model
|
marker.cutoff, estimation.method, predict.time |
function inputs |
1. Liu D, Cai T, Zheng Y. Evaluating the predictive value of biomarkers with stratified case-cohort design. *Biometrics* 2012, 4: 1219-1227.
2. Pepe MS, Zheng Y, Jin Y. Evaluating the ROC performance of markers for future events. *Lifetime Data Analysis.* 2008, 14: 86-113.
3. Zheng Y, Cai T, Pepe MS, Levy, W. Time-dependent predictive values of prognostic biomarkers with failure time outcome. *JASA* 2008, 103: 362-368.
4. Cai T. and Zheng Y . Resampling Procedures for Making Inference under Nested Case-control Studies. *JASA* 2013 (in press).
5. Cai T and Zheng Y/*, Evaluating Prognostic Accuracy of Biomarkers under nested case-control studies. *Biostatistics* 2012, 13,1, 89-100.
(* equal contributor and corresponding author).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 | #simulated data for illustration
data(SimData)
#generate a sub-cohort from SimData
set.seed(12321)
#create a sample index. 1 if sampled, 0 if not
N <- nrow(SimData)
sampleInd <- rep(0, N)
# sample all with observed failure time. (200 individuals)
sampleInd[SimData$status==1] <- 1
#sample 150 more observations from the entire data set without replacement
sampleInd[sample(1:N, 150)] <- 1
table(sampleInd) #total number of subcohort is 293
cohortData_cch <- SimData
#first calculate the Pr(Sampled from cohort) for each observation
sampleProb <- numeric(500)
#all non-censored observations were sampled, so their sample probability is 1
sampleProb[cohortData_cch$status==1] <- 1
#all other individuals had a 150/N chance to be sampled
sampleProb[cohortData_cch$status==0] <- 150/N
#the sample weights are 1/(probability of being sampled)
cohortData_cch$weights <- 1/sampleProb
#indicator of inclusion in the subcohort
cohortData_cch$subcohort = sampleInd
#estimate accuracy measures using non-parametric estimates
#by setting estimation.method = "NP"
survMTP.cch(time =survTime,
event = status,
marker = Y,
weights = weights,
subcoh = subcohort,
data = cohortData_cch,
estimation.method = "NP",
predict.time = 2,
marker.cutpoint = 0)
#estimate accuracy measures using semi-parametric estimates
survMTP.cch(time =survTime,
event = status,
marker = Y,
weights = weights,
subcoh = subcohort,
data = cohortData_cch,
estimation.method = "SP",
predict.time = 2,
marker.cutpoint = 0)
|
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