# Tagged Questions

Survival analysis is concerned with modelling the time before subjects change state, typically time until death or failure. One key feature of such data is that they can be censored, that is, some subjects will not have changed state before the study ends.

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79 views

### Testing survival against frequency of some event

I have the following data for 200 cases/subjects: time to death over a 15 year period, $t$. A datum with a value of 180 months means that the subject did not die over the 15 year period. the ...
1answer
354 views

### How to interpret the output of survival analysis?

I am beginner of survival analysis, so I am confused about some basic ideas in this area. I think the basic assumption in survival analysis is that time of event for a subject can be estimated given ...
2answers
148 views

### Difference between survival analysis and classification?

Since the time variable can be treated as a normal feature in classification, why not using more powerful classification methods (such as, C4.5, SVM) to predict the occurrence of an event? Why lots of ...
1answer
266 views

### How to run survival analysis on big dataset?

I am recently involved in a project that needs to analyze the survival time of objects. Therefore, I plan to use the rms package to build a Cox model. The problem is, since the dataset I have is so ...
2answers
702 views

### Cumulative Incidence vs. Kaplan Meier to estimate probability of failure

To estimate the probability failure in medical sciences, it is not atypical to use 1-KM. However this does not account for competing risks, such as death by natural causes or causes unrelated with the ...
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272 views

### Oddity in simulating Weibull survival times

Based on this guide to simulating survival times in SAS and R, I used the following code to generate two survival functions: ...
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159 views

### cox proportional hazard model

am doing my dissertation involving cox model and i would like to understand how you interpret the survival table at mean of covariates. how i do u i determine the survival function from the output ...
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57 views

### Inferential methods on large panel data with sparse clusters and rare outcomes

Using longitudinal survey data on children using psychotropic medications, we are interested in estimating associations with medication classes, their persistence and adherence (longitudinal ...
1answer
883 views

### Difference between survdiff log-rank and coxph log-rank

I'm using the survival package in R to analyze clinical data. I am analyzing two different groups of patients, when I calculate survdiff in order to compare the curves, I got p= 0.135, but when I ...
0answers
205 views

### Comparing Hazard Rate Ratios for different outcomes on the same sample

Suppose I have survival data coming from a cohort study. The outcome of interest is death and a subject can die either because of cancer or because of other causes. The two outcomes under study are ...
3answers
191 views

### Critical appraisal of survival paper

I must make a critical appraisal of a cancer survival paper. I hope someone here can give some hints. The paper investigates person-level markers of socio-economic status as exposure and looks for ...
2answers
202 views

### What is the difference between a hazard ratio and the e^coef of a Cox equation?

As I understand it, the definition of the hazard ratio is the ratio of two hazard rates. Often the exp(coef) from a Cox model is also used as an estimate of the hazard ratio. These methods give two ...
1answer
423 views

### Cox regression - Hazard and Survival Estimates?

I have a couple questions about Cox survival regression: 1) Is it true that the hazard function h(t) is not available (even WITHOUT time dependent covariates)- and if not, is it because the baseline ...
1answer
498 views

### P-value of a survival ROC c-index

It is possible to calculate the c-index for time dependent outcomes (such as disease) using the survivalROC package in R. My question is : is it possible to produce a p-value for the c-index that is ...
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1k views

### How to calculate predicted hazard rates from a Cox PH model?

I have the following Cox PH model (Time, Event) ~ X + Y + Z I would like to get the predicted hazard rates (i am talking about hazard rates NOT hazard ratios) ...
1answer
98 views

### Time-wise treatment effect / survival analysis

Let's say I have some kind of survival data - i.e. I'm giving a drug that may cause mortality. So I have three patients: A, B and C. All are given the drug at Time t1. Let's say patient A dies at ...
0answers
242 views

### Multiple imputation of time variables — which step to impute?

Lets assume I have a survival analysis study with an exposure, two covariates, and two time related variables. Say date of diagnosis and date of death. Combined, the two time related variables will be ...
1answer
344 views

### Floating Point Overflow while computing the Kaplan-Meier estimator in SAS

I try to estimate survival curves based on a Kaplan-Meier estimator using proc lifetest. However, SAS outputs an error message which I do not manage to circumvent. ...
1answer
391 views

### Martingale Residuals and Schoenfeld Residuals

If the Martingale Residuals indicate that a predictor $X$ violates the proportional hazards assumption but the Schoenfeld Residuals indicate that it does not....which one should you trust?
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229 views

### Proportional hazards assumption meaning

Suppose we have a Cox-PH model and death is the outcome of interest. Suppose we have the predictors $X_1, X_2$ and $X_3$. Then does the PH assumption mean that for any person (i.e. arbitrary values of ...
0answers
79 views

### Problem with lagged covariates

Suppose we have a binary variable $X$ that indicates whether a person ate pizza during the week. This variable is recorded for an entire year. So we have $X_{1}, \dots, X_{52}$ values (1 or 0). ...
1answer
258 views

### How to generate a group summary categorical variable for survival analysis in Stata?

I have registry data for which I have data for individuals for each hospital attendance over a 10 year period. I wish to determine the effect of chronic antibiotic use upon acquisition of specific ...
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121 views

### Survival analysis - help with determining source of error

I am trying to determine the effect of four interventions/exposures upon the acquisition of an infection (the interventions aimed at preventing the infection). I'm using registry data. My analysis ...
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814 views

### How to perform a Wilcoxon signed rank test for survival data in R?

Say you have survival data like this: ...
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2k views

### Interpretation and validation of a Cox proportional hazards regression model using R in plain English

Can someone explain my Cox model to me in plain English? I fitted the following Cox regression model to all of my data using the cph function. My data are saved in an object called "Data". The ...
1answer
259 views

### Robust variance/covariance matrix in Poisson regression

Suppose I have survival data with more than one row per subject, because I have splitted the follow-up time of each subject into pieces (maybe because I have one or more time-varying variables or ...
1answer
82 views

### Best terminology to describe a time-series problem

I have a problem that I would like to investigate regarding time-series data, but as I'm inexperienced in the field of statistics, I am unsure of the best terminology to describe my problem (so I can ...
0answers
91 views

### Probability calculation in survival analysis

I have 13 similar independent units and I need to calculate the probability at least 6 of them to survive for time less than 1.10. From a table with the Kaplan-Meir estimates I get the following; ...
1answer
320 views

### Stratified Cox model

I am working on fitting a Cox model to predict. But several predictors violated the proportional hazards assumption. I am gonna to do stratified Cox model to adjust them. But the results of stratified ...
1answer
875 views

### How to do cross-validation with a Cox proportional hazards model?

Suppose I have constructed a prediction model for the occurrence of a particular disease in one dataset (the model building dataset) and now want to check how well the model works in a new dataset ...
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371 views

### Sample size and cross-validation methods for Cox regression predictive models

I have a question I would like to pose to the community. I have recently been asked to provide statistical analysis for a tumor marker prognostic study. I have primarily used these two references to ...
1answer
1k views

### Different prediction plot from survival coxph and rms cph

I've created my own slightly enhanced version of the termplot that I use in this example, you can find it here. I've previously posted on SO but the more I think about it I believe that this probably ...
0answers
253 views

### What data structure is necessary for survival analysis?

I'm relatively new to survival analysis and try to get my data in the right shape. I have two tables both concerning the observed individuals. If I just would use one of the tables, I would have ...
1answer
175 views

### What statistic test apply to a cell count time line?

I am a PhD student with some difficulties about what test to choose to verify an experiment. Hope you can give me some help! My experiment: I am counting the number of a subset of cells in Drosophila ...
3answers
217 views

### Survival analysis with categorical variable

I have event time data for subjects with different categories (A, B, C etc.) yearly observed. To my understanding my data is both right and interval censored (?). Subjects' category can change from ...
1answer
293 views

### Predicting the time until an expected event occurs

I have a situation where an event is supposed to occur every x minutes for a number of different sites (each site could be configured for a different time interval x). From time to time the event may ...
1answer
146 views

### Compare survival of one population to the general population

I have the survival dataset of a population with a special disease. I´d like to compare this population with the general population to see whether this population has a decreased life-expectancy ...
1answer
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### Inconsistency of the Breslow estimator

The Breslow estimate is commonly used in the Cox proportional hazards model. However this paper by Deborah Burr Burr, D. (1994). On Inconsistency of Breslow's Estimator as an Estimator of the ...
0answers
133 views

### Variance of the Kaplan-Meier estimate for dependent observations

Can someone help me find a way to estimate the variance of the Kaplan-Meier estimate with dependent observations? Specifically, I have failure time data from patients with several different ...
1answer
133 views

### Are survivor functions meaningful with proportional hazards models?

Does the survivor function estimated after running a Proportional Hazards model give valid predicted probabilities of an event happening after a number of time periods? The only source I've found on ...
3answers
198 views

### Understanding survival at time function

This question is related to a few others (Here,Here) on the topic as I have been searching for information. Hopefully this one is sufficient. 1) I am seeing differences in the relationship between ...
1answer
274 views

### How can I censor entries at failure or an exit age in STATA?

I am attempting to construct a survival analysis in STATA whereby subjects fail if the failure condition is met (Staph) but are also removed from the model once they are over 1100 days old. My ...
1answer
255 views

### How can I display a survival curve with right censoring marks?

I have the following survival data and have constructed a survival plot however cannot mark the right censored points (which makes me think my survival graph is also incorrect) - how can I manage this ...
2answers
224 views

### What happens if a survival curve doesn't reach 0.5?

Does this mean you can't compute the median?
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### How do you plot survival functions for specific values of covariates in SAS?

Suppose I do the following: proc phreg data = new; model time*censor(0) = x y; run; Also suppose $x$ is a binary variable and $y$ is a ...
1answer
398 views

### SAS Code for Survival Analysis

In PROC PHREG, how do you set a continuous variable at a certain value as the reference level? For example, suppose x = 3.5, 3.6, 4.3, 5.4 and we want x = 6 to be the reference level. How would you do ...
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249 views

### Proportional hazards assumption

The proportional hazards assumption basically says that the hazard rate does not vary with time. That is, $\text{HR}(t) \equiv \text{HR}$. When can we assume this? What if the hazard ratios at ...
3answers
917 views

### Finding median survival time from survival function

Is the best way to find the median survival time from a survival plot just to draw a horizontal line from $p = 0.5$ to the curve and project down to the x-axis?
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2k views

### Time dependent coefficients in R - how to do it?

Update: Sorry for another update but I've found some possible solutions with fractional polynomials and the competing risk-package that I need some help with. The problem I can't find an easy way ...
1answer
196 views

### Sampling distribution is skewed in a fully Bayesian inference of MCMC in Cox PH models

I used the MCMC method to estimate linear models with a fully Bayesian inference previously, and had no problem from estimated coefficients. Recently I use the same way in a semiparametric Cox PH ...
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