Estimating sample size for Cox Proportional Hazards

[Leah Jacobs]

Hello and thank you, in advance, for any assistance!

I am in the design phase for a longitudinal study examining the effect of a predictor (neighborhood risk score) on time to an outcome (re-arrest), as well as whether or not the variation explained by the predictor is moderated by membership in one of two independent groups (those with substance use disorders vs. those without). Because the data is censored (I'm only observing for 12 months), I intend to use a proportional hazard model. I also intend to control for several addition covariates (risk factors). 

I have read multiple methodological articles on power calculation and I still feel totally directionless. At present, I have data from the study population on the proportion of individuals who have the outcome vs. those who do not have the outcome within 12 months. I also have data on the proportion of the study population who fall into each of the groups of interest. I do not have the standard deviation for these values, nor do I have data on the covariates. 

Any assistance with the above or suggestions for easy to understand guides are much appreciated.

Best,

Leah

[Lenth, Russell V]

I do not have much experience with these types of models, so I can't help much. I think that not many people are available in this group. May I suggest that you post the same question in stats.stackexchange.com? That is a really active forum and you're much more likely to get experienced advice there.

Russ

Sent from my iPad

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[Leah Jacobs]

thank you for the suggestion.