[Cox proportional hazards regression][1] is a very popular, semi-parametric method for survival analysis.

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Why is the derivative not zero?

I am working with survival models and I am using R's coxph function to learn the Cox proportional hazard model. To try it out, I am using the standard veteran dataset (obtainable by loading the ...
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Time-dependent coxph output and making predictions in R

I'm trying to use a Cox proportional hazard model to predict the time until an employee terminates from an organization. There are a bunch of covariates (~20), some of them time-dependent. So I've ...
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8 views

Point process models

Two of the popular models for analyzing point process data are Cox and Hawkes processes. My question is how do we compare the statistical properties of these two processes as they both can be ...
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15 views

Exp(b) in multivariate Cox regression

I am trying to interpret the results of a Cox regression. I ran a multiple Cox regression analysis of an categorical variable—heart rate including 5 levels. I added covariates that were also ...
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22 views

How to visualize a significant interaction between two linear predictors using the rms package?

Two linear predictors interact significantly (see below). How can I visualize this interaction in a plot? ...
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23 views

Different quantile values for a predictor between the root data and and the data of a Predict() object

I want to plot a continous predictor using restricted cubic splines and indicating the distribution of the linear predictor using a box-and-whisker plot. However, the quantile values differ from those ...
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8 views

Cox model with known measurement error

I am trying to perform a univariate Cox PH survival analysis in R. My covariate was generated from another analysis, meaning that I have a 95% CI range (between 0 and 1) for the values. Right now, I ...
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1answer
37 views

Comparing regression models with different coding of the same linear predictor

How can I determine whether one coding of a linear predictor leads to a better fit of the corresponding regression model than the other? In the following example, the restricted cubic spline coding of ...
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18 views

Cox Time Series Data — Analysis of Interaction Terms

In a time series data set using Cox Proporational Hazard Rate, I am testing a model with interaction terms. I am worried that my interaction term is biased by several specifications of my model and I ...
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2answers
131 views

Comparing a linear model with a spline model

I try to figure out how to describe my continuous variable. Unfortunately, I did not understand all of the statistics. I would really appreciate I you guys would help me out here. To better illustrate ...
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21 views

Cox survival analysis versus multilevel modeling

I'm debating the wisdom of a couple different approaches. I am constructing a model that measures whether the amount of a treatment received leads to a person coming back for another treatment or ...
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1answer
33 views

Difference between multi-factor ANOVA and Cox proportional hazard model?

I am wondering what is the difference between multi-factor ANOVA and Cox proportional hazard model? As I understood both of them test the significance of some independent factors on a dependent ...
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55 views

How to simulate informative censoring in a Cox PH model?

I wish to simulate events from a Cox PH model where the censoring is informative, and to compare parameter estimator quality with estimates obtained from data generated by a Cox PH model with ...
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1answer
52 views

Interpretation Interaction in Cox Regression

I am estimating a discrete choice model with the help of cox regression in SPSS. I would like to interact two continuous predicting variables. The main effect of one of the ineracting variables is ...
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13 views

What are easy steps of finding cutpoint in continuous variable with Time to event outcome, in Stata?

I find it painful to manually guess a dichotomized cutpoint predictor (continuous) for an time to event outcome in Simple Cox proportional hazard model. Currently I was trying to find the cutpoint ...
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15 views

Very puzzling - naming the endpoint of survival analysis

A question that should be straightforward for statisticians but is puzzling me to the point I am nervous. I am doing a PhD in Epidemiology and am going to use Cox regression. The predictor is a ...
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1answer
68 views

Analyzing seasonality in data

In order to analyze the data in presence of seasonality, I used two methods: Proportional hazard model (Cox model) and time series method (Triple Exponential Smoothing (Holt Winters Method)). Now , my ...
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17 views

Comparing Cox models

We want to compare different methods of modelling a continuous covariate (X) in a Cox model. For example, in the first model we use X in its continuous form. In a second model we categorize X into ...
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21 views

bias of an estimator when the variable is categorical

I want to calculate the bias of the coefficient estimate (beta hat) in Cox regression. But for a categorized variable, for example using quantiles we define a variable with 4 categories, then the ...
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1answer
57 views

Get survival rates from a cox regression in R

I am fairly new to survival analysis and am playing around in R. I have a fairly simple cox model ...
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1answer
80 views

Univariate cox regression hazard ratio in SPSS

I'm currently doing some analysis for a retrospective cohort study of biomarkers in cancer patients. I've noticed that some papers have utilized univariate cox regression analysis to generate a hazard ...
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22 views

Parameter estimates from extended cox model using the coxph() function from the survival package in R

I want to understand how the parameters from a Cox Model using the coxph() function from the survival package in R are estimated. I am following a book by Rizopoulos [1]. In the book the partial log ...
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14 views

covariate-adjusted analysis for time to event endpoint in a cross over design RCT

I have a time to event endpoint in a 2x2 crossover RCT which I would like to analyse with a regression model to adjust for covariate effects. I am supposing I cannot fit a Cox proportional Hazards ...
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1answer
30 views

Risk ratios in a Cox hazard model

I'm reading a paper which gives "Risk ratios from Cox hazard models with time-varying covariates". Time-varying covariates just means that, for example if $X_i$ is a covariate for person $i$ then it ...
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1answer
81 views

Post-hoc power size calculation

I have, probably, a simple problem. I've finished analysing the results of an observational prospective study conducted in our unit. In this study I evaluated if a specific biomarker is independently ...
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How to interpret the R output of anova.coxph

The likelihood ratio chi^2 test is the gold standard for comparing nested Cox models. However I am not sure how to interpret the R output. ...
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38 views

Time varying coefficient in cox model

I have a model for survival after an injury that is borderline passing the Schoenfeld test for the proportional hazards assumption (cox.zph() in R). However, ...
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How to do Cox regression if we have a variable which violates an assumption?

Is there a better way than stratification to do Cox regression for two variables, one qualitative and other quantitative, the qualitative (and more important one) violates an assumption of Cox ...
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1answer
38 views

Cox Regression: Testing for effect in subgroup

I'm using a cox proportional hazard model in R to see if a treatment variable (treatment or placebo) has effect on the survivaltime of patients. I intend to test this for each of my grouping variables ...
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25 views

Simple Cox-related question regarding the LR test

I'm writing the Results section of a paper: If the LR-test for a Cox proportional hazards model is not significant, but one of the predictors is significant, does one (usually) report the covariate's ...
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22 views

Predict Kaplan-Meier Curve from Hazard Ratios

For illustration purposes I want to plot some potential hazard ratios, based on a known proportional hazard model. For example, plot the known curve, then plot what the curve may look like with HR's ...
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1answer
38 views

Relative Risk with Log-rank test

I always associated/used log-rank test to evaluate Hazard Ratios. However, a well-known professor is using/presenting results of log-rank test for Relative Risk and Risk Ratio. Can anyone explain ...
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How to fit cox ph model in R to pre aggregated data

What I mean is suppose instead of individual observations one has only grouped data like this: Month,Age,Height,NoOfObseravtions,DeathRate 1,20-25,5.5-6.0,100,1% 1,20-25,5.5-6.0,150,1.20% ...
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19 views

Extracting univariate regression for multiple predictors into one table

I am doing univariate Cox regression for multiple variables: ...
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1answer
60 views

Cox-Proportional hazards model with panel (longitude ) data

I am working with panel data with incomplete case: and the goal is to predict the probability of 1 at each time for each case. I am trying to use the cox-ph model for this analysis because like ...
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Does fitting Cox-model with strata and strata-covariate interaction differ from fitting two Cox models?

In Regression Modeling Strategies by Harell there is a section (S. 19.1.7) discussing Cox models including an interaction between a covariate whose main effect on survival we want to estimate as well ...
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Temporal features in survival analysis

I'm modeling customer churn, experimenting with both Aalen Additive and Cox Proportional Hazards models, using the lifelines package in Python. If this were a more ...
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68 views

What is the right way of computing baseline hazard rate

What is the right way of computing baseline hazard rate? To my understanding hazard rate at time t is simply #events / #AtRisk ...
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Check hazard proportional assuption in a large coxph

I would like to check hazard proportional assuption in a large coxph. Usually I check it with cox.zph but with large coxph my p-value are very small whereas the log(-log(S(t)) curves are almost ...
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24 views

Interpretation of non-significant parameters in significant Cox-model as prognostic factors

I want to analyze predictive factors for patient survival after surgery. I have variables that are based on investigations at the time of the surgery, known predictive factors (age, KPS) and data on ...
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33 views

P-value from proportional hazards regression object [closed]

I'm running some proportional hazards regression models using the survival package in r and would like to know how I can access ...
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1answer
45 views

Dummy variables and intercept in Cox regression

I am working with the Cox Proportional Hazards model. Where the covariates include 2 categorical variables. Assume each category has 3 levels, so I model these in terms of dummy variables. Category ...
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1answer
16 views

Comparing survival times in small samples for two groups

I am working on a dataset of big cats. 18 cats have a particular antigen and the rest (58) do not. We have contact times for when blood samples were taken - so when the cats were identified as having ...
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1answer
140 views

Interpretation of the hazard ratio in a spline model on continuous exposures

I am having trouble interpreting the output from a Cox proportion hazard model with a spline term on a continuous exposure. In the below example (pseudo-code from ...
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1answer
68 views

how to interpret log transformed variables in survival analysis?

Suppose I have the following models: fit1 <- coxph(Surv(y,cov)~x,data=records) and ...
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Survival analysis coxph using ridge regression with 2000 variables => “Penalty terms cannot be in an interaction”

I'm doing a survival analysis using coxph function (package survival). I'm using a ridge regression model included 2000 variables but I have a type of error message "...
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2answers
66 views

Different “end of study” times for different cohorts - Cox PH model in survival analysis

I have a dataset with 4 cohorts of about the same size (~700 people each). I'm trying to apply a Cox PH model using the time needed to pass a very difficult exam as my "time" variable. The cohorts ...
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1answer
34 views

Proportionality assumption test (SAS) for categorical predictors

For Cox regression with all categorical predictors, I want to model time-dependent covariates (time*cov in Proc PHREG) to ...
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1answer
25 views

Can you use event history analysis if your sample was selected on the dependent variable?

I have a dataset that includes a random sample of individuals who are currently in a relationship in the United States. I also have data on the date that they met their partner and the date that they ...
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ROC and post estimation COX Harrell's C using your dataset

I have built a predictive model using a combination of logistic and cox regression models. I did it using a dataset of about 5000 records. I would like to calculate the AUC and the Harrell's post ...