# Tagged Questions

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9 views

### A strange finding with the logrank test statistics

When I try to confirm the type I error rate of the logrank test by simulation, I found something strange... Firstly, I generated 100 observations from exponential distribution with lamda1=1 as group 1 ...
8 views

### p-value of logrank test with three groups

I faced with the following situation. There are 3 groups in my data and I am to compare pairwise these groups and obtain logrank p-value. If I am to compare say 1 and 3 groups should I remove the 2nd ...
21 views

### Poisson regression, negative binomial or log-rank test in survival analysis

I want to know which test should I use on the following data: I counted the number of events per person over a 4 year period (2007-2011). I created different groups which are: ...
10 views

### A simple question about log-rank test

I am learning log-rank test for performing survival analysis. I read article "Statistics review 12: Survival analysis", section "Comparing survival curves of two groups using the log rank test". ...
52 views

### Can coxph be used for categorical data?

I'm doing some survival analysis and I got the idea to change a binary variable into three-category variable by sub-dividing one category of the binary variable into two new categories. Here's a ...
14 views

### The effect of prognostic factors on the power in survival analysis

I was curious to know if there exists closed form equations for calculating the power in survival analysis, using either Cox-regression or the log-rank test, when their is an important prognostic ...
32 views

### Version of Mann-Whitney U test, for right-censored data

Is there an equivalent of the Mann-Whitney U test, but for right-censored data? I have right-censored numerical data from two different groups. The mean for one group is higher than the other. I'd ...
40 views

### log-rank test for unbalanced group sizes

We have clinical data (survival times) and a list of features for each patient and want to come up with a stratifier that has a low (log-rank) p-value. Is there a way to avoid stratifiers that lead to ...
108 views

### one-sided survival log rank test p-value

I want to compare two treatments for an oncology indication. I used a log rank test as two treatments (variable treatment) with time (variable month) and censor status (variable censor). Below is the ...
17 views

### Should stratified analyses be used when stratified randomization has been used?

I am considering a randomised controlled trial (RCT) where an experimental intervention A is compared to a bag of standard treatments, B, C and D (which range from intensive to minimal active ...
64 views

### how can I focus the log rank test in a selected period of time of follow up?

I am using R survdiff (survival package). I would like to focus the analysis on the first 2 years of my survival curve (that is actually much longer, but with few cases in the long term and with ...
11 views

### Uneven (right) censoring where the time of truncation is constant

I've collected data comparing the relative success of two different groups of participants on finding the answer to a difficult question. The problem is that not all the participants in the control ...
19 views

### Is there a reason chi square tests are used over normal tests in survival?

I've been reading and programming a bit about survival, and it seems that a lot of statistics are normally distributed (and thus, their square is chi square distributed). For example, the log rank ...
47 views

### Reproducing the cox model score test in R

I am using R and would like to recreate by hand the values of the tests. For example, ...
273 views

### Survival analysis: log rank or ANOVA to compare groups?

If I want to know whether there is a significant difference in age of onset between the 2 groups, should I use ANOVA? My data meet the requirements of an ANOVA test. Or should I use the log rank test, ...
217 views

### One-Sample Log-rank test statistic

Ok, I am totally confused, this is probably a pure math rather than a statistic question but please enlighten me. I found the logrank statistic formula being reported in the literature in 2 ways, but ...
88 views

### What is the R code for a 2 one-sided equivalence log-rank test? [closed]

I am trying to perform an equivalence test (alpha = 0.1, beta = 0.8, equivalence interval = 0.85-1.25) for two samples of survival data. Is there a code in R in the Survival package or any other ...
77 views

### How can you have p < 0.0001 with a sample size of 89 and a control group of 52?

From Efficacy of monoterpene perillyl alcohol upon survival rate of patients with recurrent glioblastoma (linked from Does Frankincense cure cancer?): Patients and methods It was included 89 ...
129 views

### Survival probability for a case-control study

I have a case-control study in which 21 patients with a certain clinical outcome and 20 patients without that clinical outcome were (retrospectively) selected from a larger group of patients who were ...
24 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 ...
82 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 ...
313 views

### Matlab survival curve log rank test

I am trying to do survival analysis in matlab and want to calculate log rank test scores among several curves. I found a possible code to do log rank here. But based on its description, it can only do ...
2k views

### How to calculate the HR and 95%CI using the log-rank test in R?

The R survival package is very useful to do survival analysis. And I know the survdiff function can be used to compare the difference of survival time in two or more groups. And the p-value number can ...
593 views

### Log-rank / Cox analysis with very unequal sized groups: alternative calculations of p-value?

I would like to set up a series of tests on the difference in survival between two very unequal sized groups. Generally either log-rank (using the R survdiff function) or a cox regression (R coxph) ...
2k views

### log-rank test in R

I need to use the survdiff function to statistically compare (using log-rank test) the following survival functions: (1) Male (Sex=1) and Female (Sex=2) (2) ...
420 views

### Logrank test for trend (proportional hazards)

How one can create a logrank test for trend and does it differ from normal logrank test? Any suggestions or literature? Maybe some R examples and functions?
145 views

### Validity of Log-rank p-value when there are zero events in one group?

I am looking to do a Kaplan Meier analysis to look at survival in two groups. I have 21 people in group A and 17 people in group B. 5 people in group B died at various times, 0 people in group A died, ...
1k views

### Sample size / power calculation for logrank survival test

I have really little idea of survival analysis. I am aware that logrank is a special case of Cox' proportional hazards model, and that tons of R packages and scripts address the problem of power / ...
67 views

### Error in books formula concerning the log-rank test?

I am currently reading the following book: Clinical Trials: A Practical Guide to Design, Analysis, and Reporting by Duolao Wang, Ameet Bakhai (2006) On page 243-244 there is an example about the ...
741 views

### In which situation does the log-rank test have low power?

This question is complementary to question 1 asked by @Jesse here. It is about the case when we don't find a significant result when performing the log-rank test and when the proportional hazard ...
297 views

### KM curve: log rank test significant but HR crosses 1

Hello and thanks for this source about statistics. My Problem is about a situation where Kaplan Meier curves differ in meaning of a significant log rank test, but the hazard ratio crosses 1 when ...
403 views

### Combining several survival experiments

In four independent experiments, two strains (A and B) were compared in their respective survival curves. Two experiments show a clear-cut result (A survives at 100%, almost half B dies). Two further ...
6k 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 ...
325 views

### How do I compare 2 models?

I would like to show that a new biomarker (let's say percent tumor volume reduction at 3 weeks of treatment estimated with automatic methods) performs better than an old one (same measure, but based ...
2k views

### How best to analyze length of stay data in a hospital-based RCT?

I am interested in knowing whether or not there is a consensus about the optimal way to analyze hospital length of stay (LOS) data from a RCT. This is typically a very right-skewed distribution, ...
1k views

### Which algorithm to compute p-value of logrank test with three or more groups is best?

There seem to be two different algorithms for comparing three or more survival curves using the logrank test. Algorithm A. Found in books by Altman and Machin. Computed by GraphPad Prism. This ...