Publications by Keith Goldfeld
Bayesian proportional hazards model for a stepped-wedge design
We’ve finally reached the end of the road. This is the fifth and last post in a series building up to a Bayesian proportional hazards model for analyzing a stepped-wedge cluster-randomized trial. If you are just joining in, you may want to start at the beginning. The model presented here integrates non-linear time trends and cluster-specific rand...
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Accounting for ties in a Bayesian proportional hazards model
Over my past few posts, I’ve been progressively building towards a Bayesian model for a stepped-wedge cluster randomized trial with a time-to-event outcome, where time will be modeled using a spline function. I started with a simple Cox proportional hazards model for a traditional RCT, ignoring time as a factor. In the next post, I introduced a n...
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A Bayesian proportional hazards model with a penalized spline
In my previous post, I outlined a Bayesian approach to proportional hazards modeling. This post serves as an addendum, providing code to incorporate a spline to model a time-varying hazard ratio non linearly. In a second addendum to come I will present a separate model with a site-specific random effect, essential for a cluster-randomized trial. Th...
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Estimating a Bayesian proportional hazards model
A recent conversation with a colleague about a large stepped-wedge design (SW-CRT) cluster randomized trial piqued my interest, because the primary outcome is time-to-event. This is not something I’ve seen before. A quick dive into the literature suggested that time-to-event outcomes are uncommon in SW-CRTs-and that the best analytic approach is ...
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Thinking about covariates in an analysis of an RCT
I was recently discussing the analytic plan for a randomized controlled trial (RCT) with a clinical collaborator when she asked whether it’s appropriate to adjust for pre-specified baseline covariates. This question is so interesting because it touches on fundamental issues of inference—both causal and statistical. What is the target estimand i...
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Can ChatGPT help construct non-trivial statistical models? An example with Bayesian “random” splines
I’ve been curious to see how helpful ChatGPT can be for implementing relatively complicated models in R. About two years ago, I described a model for estimating a treatment effect in a cluster-randomized stepped wedge trial. We used a generalized additive model (GAM) with site-specific splines to account for general time trends, implemented using...
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An IV study design to estimate an effect size when randomization is not ethical
An investigator I frequently consult with seeks to estimate the effect of a palliative care treatment protocol for patients nearing end-stage disease, compared to a more standard, though potentially overly burdensome, therapeutic approach. Ideally, we would conduct a two-arm randomized clinical trial (RCT) to create comparable groups and obtain an ...
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Generating binary data by specifying the relative risk, with simulations
The most traditional approach for analyzing binary outcome data is logistic regression, where the estimated parameters are interpreted as log odds ratios or, if exponentiated, as odds ratios (ORs). No one other than statisticians (and maybe not even statisticians) finds the odds ratio to be a very intuitive statistic, and many feel that a risk diff...
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simstudy: another way to generate data from a non-standard density
One of my goals for the simstudy package is to make it as easy as possible to generate data from a wide range of data distributions. The recent update created the possibility of generating data from a customized distribution specified in a user-defined function. Last week, I added two functions, genDataDist and addDataDist, that allow data generati...
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simstudy 0.8.0: customized distributions
Over the past few years, a number of folks have asked if simstudy accommodates customized distributions. There’s been interest in truncated, zero-inflated, or even more standard distributions that haven’t been implemented in simstudy. While I’ve come up with approaches for some of the specific cases, I was never able to develop a general solu...
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