# cox

1. ### How to deal with non-proportional hazard Cox models?

Dear all, I want to run a Cox model to see if there is an interaction between two treatments. However, the test to see if proportional hazard is respected suggests that it is actually not respected. So I don't know what other statistical survival analysis to do because it means I cannot rely on...
2. ### Survival analysis at few dates: glms? logrank? cox ?

Hello, In many documentation I have read that Kaplan-Meier curves followed by logrank test and/or cox models are the most recommended statistical methods to analyse Survival and test for different factors that may impact the Survival. However, I have also heard that these are suitable if I...
3. ### Cox proportional hazard analysis with non-uniform samples; power analysis

We have a study involving 10000 patients, 5000 of them treated with drug A and 5000 with drug B. We want to know if drug A is more effective than B. The median time to event (death) after treatment with drug A is 1000 days and for drug B it is 2000 days. There are two sampling scenario: In...
4. ### How to do power analysis

I want to do power analyses prior doing statistical tests on data to assess for the power it would yield. It mostly is survival data. I want to use Cox etc. What will you recommend, how to perform these?
5. ### Cox's regression

Hello, I have some experimental data for animals with tumours. Unfortunately, they were not followed individually during a time course, but evaluated as groups. As a result, I have 6 predictors only for animals that have survived for each time point. I would like to test which of these...
6. ### Conflicting Results Evaluating Proportional Hazards Assumption

Hello, Currently working on a survival analysis of some lung cancer patients. I am building a Cox PH model and was working on validating the PH assumption for my covariates. To do this am using two techniques. Looking at the -log(-log(s)) plot of the survival function and also looking at the...
7. ### Cox Proportional hazard model result interpretation

Could anyone please help me to interpret results from Cox Proportional hazard model result interpretation.:wave: I am using SAS ENTERPRISE Guide and I have the following results: Analysis of Maximum Likelihood Estimates (shown in the image)
8. ### number of variables for a model

I am now trying to build a cox model: h(t, beta) = h0(t)exp(X*beta) I have selected some variables from the data, and for a category variable, if it contains N categories, I will set up N-1 dummy variables for it, if so, there are 26 variables in my model, is it too many for a model? But...
9. ### cox model with time dependent covariate

I am trying to fit a cox model: h(t, beta) = h0(t)exp(X*beta), while X = (x1, x2, ..., xN) but, for instance, x1 is binary with value of 0 or 1, but the hazard ratio of 1 and 0 is not proportional: t: 1 2 3 4 5 6 7 .... hazard ratio: 0.2 0.3...
10. ### SPSS Cox regression analysis

Hi, I'm a student at university doing my dissertation project. I'm looking at what could independently predict readmission to hospital. We have done a cox regression analysis but the results seem to be the wrong way. It shows that a factor increases the likelihood of readmission but when...
11. ### What if events also have factors, not only the studied subjects!!

Hello everyone... despite my a little knowledge in survival analysis and its available models.... I have the following question: What I know that Cox models offer a hazard function, with the assumption of proportionality of the hazard for different studied subjects. The frailty component...
12. ### 1 predictor, 2 different values for baseline statistic & change statistic?

Hi, I am conducting a Cox Regression for my first time. I created a simple model with only 1 predictor (categorical), one dependent variable (continuous survival time), and 1 event that defines whether the hazard criterion was met (dichotomous). Since there is only one step in this model, I...
13. ### How to draw cubic splines after Cox regression in Stata 11.1?

Hi everyone:), In a cohort study, I would like to draw cubic splines, including HR and 95% CI, after Cox regression adjusted for age and sex. Yet, I have not found out the solution:confused:. Suppose that there are variables as follows: observetime, censor, variablex (the independent...
14. ### Cox Proportional Hazards Assumption Question

I have a dataset of cancer cases from 1997 to 2007. I am performing a Cox Model on this set of cases. However, I just realized that mortality rates and the raw number of deaths are decreasing. Does anyone have an opinion as to whether a non-constant death rate over time will violate any Cox...
15. ### Question about a strange type of variable in Cox regression table

I have a question about this Cox regression analyse table; If you take a look at the valuation of variables in this table, you will see that some are coded binair (0 or 1). But for some reason the author of this table used for 'tooth type' a valuation from 1 to 6. So my questions are; Is...
16. ### Survival Analysis: Cox Proportional Hazards with 4000 indicator variables

THE SITUATION: I am preparing a 420,008 observation Cox Proportional Hazards Regression model with 4001 indicator variables. The 4001st indicator is my baseline. I am using STATA to accomplish this task, but STATA/IC's maximum number of indicators it can generate is set at 2000. Further, the...