# Articles by Keith Goldfeld

### Framework for power analysis using simulation

March 15, 2021 |

The simstudy package started as a collection of functions I developed as I found myself repeating many of the same types of simulations for different projects. It was a way of organizing my work that I decided to share with others in case they want...

### Randomization tests make fewer assumptions and seem pretty intuitive

March 1, 2021 |

I’m preparing a lecture on simulation for a statistical modeling class, and I plan on describing a couple of cases where simulation is intrinsic to the analytic method rather than as a tool for exploration and planning. MCMC methods used for Bayesi...

### Visualizing the treatment effect with an ordinal outcome

February 15, 2021 |

If it’s true that many readers of a journal article focus on the abstract, figures and tables while skimming the rest, it is particularly important tell your story with a well conceived graphic or two. Along with a group of collaborators, I am tryi...

### How useful is it to show uncertainty in a plot comparing proportions?

February 1, 2021 |

I recently created a simple plot for a paper describing a pilot study of an intervention targeting depression. This small study was largely conducted to assess the feasibility and acceptability of implementing an existing intervention in a new popu...

### Finding answers faster for COVID-19: an application of Bayesian predictive probabilities

January 18, 2021 |

As we evaluate therapies for COVID-19 to help improve outcomes during the pandemic, researchers need to be able to make recommendations as quickly as possible. There really is no time to lose. The Data & Safety Monitoring Board (DSMB) of COMPIL...

### Coming soon: effortlessly generate ordinal data without assuming proportional odds

January 4, 2021 |

I’m starting off 2021 with my 99th post ever to introduce a new feature that will be incorporated into simstudy soon to make it a bit easier to generate ordinal data without requiring an assumption of proportional odds. I should wait until this fea...

### Constrained randomization to evaulate the vaccine rollout in nursing homes

December 21, 2020 |

On an incredibly heartening note, two COVID-19 vaccines have been approved for use in the US and other countries around the world. More are possibly on the way. The big challenge, at least here in the United States, is to convince people that these...

### A Bayesian implementation of a latent threshold model

December 7, 2020 |

In the previous post, I described a latent threshold model that might be helpful if we want to dichotomize a continuous predictor but we don’t know the appropriate cut-off point. This was motivated by a need to identify a threshold of antibody leve...

### A latent threshold model to dichotomize a continuous predictor

November 23, 2020 |

This is the context. In the convalescent plasma pooled individual patient level meta-analysis we are conducting as part of the COMPILE study, there is great interest in understanding the impact of antibody levels on outcomes. (I’ve described variou...

### Exploring the properties of a Bayesian model using high performance computing

November 9, 2020 |

An obvious downside to estimating Bayesian models is that it can take a considerable amount of time merely to fit a model. And if you need to estimate the same model repeatedly, that considerable amount becomes a prohibitive amount. In this post, w...

### A refined brute force method to inform simulation of ordinal response data

October 26, 2020 |

Francisco, a researcher from Spain, reached out to me with a challenge. He is interested in exploring various models that estimate correlation across multiple responses to survey questions. This is the context: He doesn’t have access to actual dat...

### simstudy just got a little more dynamic: version 0.2.1

October 12, 2020 |

simstudy version 0.2.1 has just been submitted to CRAN. Along with this release, the big news is that I’ve been joined by Jacob Wujciak-Jens as a co-author of the package. He initially reached out to me from Germany with some suggestions for improv...

### Permuted block randomization using simstudy

September 28, 2020 |

Along with preparing power analyses and statistical analysis plans (SAPs), generating study randomization lists is something a practicing biostatistician is occasionally asked to do. While not a particularly interesting activity, it offers the oppo... [Read more...]

### Generating probabilities for ordinal categorical data

September 14, 2020 |

Over the past couple of months, I’ve been describing various aspects of the simulations that we’ve been doing to get ready for a meta-analysis of convalescent plasma treatment for hospitalized patients with COVID-19, most recently here. As I contin...

### Diagnosing and dealing with degenerate estimation in a Bayesian meta-analysis

August 31, 2020 |

The federal government recently granted emergency approval for the use of antibody rich blood plasma when treating hospitalized COVID-19 patients. This announcement is unfortunate, because we really don’t know if this promising treatment works. The...

### Generating data from a truncated distribution

August 17, 2020 |

A researcher reached out to me the other day to see if the simstudy package provides a quick and easy way to generate data from a truncated distribution. Other than the noZeroPoisson distribution option (which is a very specific truncated distribution), there is no way to do this directly. You ...

### A hurdle model for COVID-19 infections in nursing homes

August 3, 2020 |

Late last year, I added a mixture distribution to the simstudy package, largely motivated to accommodate zero-inflated Poisson or negative binomial distributions. (I really thought I had added this two years ago - but time is moving so slowly these days.) These distributions are useful when modeling count data, but ...

### A Bayesian model for a simulated meta-analysis

July 20, 2020 |

This is essentially an addendum to the previous post where I simulated data from multiple RCTs to explore an analytic method to pool data across different studies. In that post, I used the nlme package to conduct a meta-analysis based on individual level data of 12 studies. Here, I am presenting ...

### Simulating multiple RCTs to simulate a meta-analysis

July 6, 2020 |

I am currently involved with an RCT that is struggling to recruit eligible patients (by no means an unusual problem), increasing the risk that findings might be inconclusive. A possible solution to this conundrum is to find similar, ongoing trials with the aim of pooling data in a single analysis, ...