Publications by Keith Goldfeld
simstudy updated to version 0.1.14: implementing Markov chains
I’m developing study simulations that require me to generate a sequence of health status for a collection of individuals. In these simulations, individuals gradually grow sicker over time, though sometimes they recover slightly. To facilitate this, I am using a stochastic Markov process, where the probability of a health status at a particular ...
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Analyzing a binary outcome arising out of within-cluster, pair-matched randomization
A key motivating factor for the simstudy package and much of this blog is that simulation can be super helpful in understanding how best to approach an unusual, or least unfamiliar, analytic problem. About six months ago, I described the DREAM Initiative (Diabetes Research, Education, and Action for Minorities), a study that used a slightly innov...
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Simulating an open cohort stepped-wedge trial
In a current multi-site study, we are using a stepped-wedge design to evaluate whether improved training and protocols can reduce prescriptions of anti-psychotic medication for home hospice care patients with advanced dementia. The study is officially called the Hospice Advanced Dementia Symptom Management and Quality of Life (HAS-QOL) Stepped We...
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There’s always at least two ways to do the same thing: an example generating 3-level hierarchical data using simstudy
“I am working on a simulation study that requires me to generate data for individuals within clusters, but each individual will have repeated measures (say baseline and two follow-ups). I’m new to simstudy and have been going through the examples in R this afternoon, but I wondered if this was possible in the package, and if so whether you co...
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Selection bias, death, and dying
I am collaborating with a number of folks who think a lot about palliative or supportive care for people who are facing end-stage disease, such as advanced dementia, cancer, COPD, or congestive heart failure. A major concern for this population (which really includes just about everyone at some point) is the quality of life at the end of life and...
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Any one interested in a function to quickly generate data with many predictors?
A couple of months ago, I was contacted about the possibility of creating a simple function in simstudy to generate a large dataset that could include possibly 10’s or 100’s of potential predictors and an outcome. In this function, only a subset of the variables would actually be predictors. The idea is to be able to easily generate data for ...
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What can we really expect to learn from a pilot study?
I am involved with a very interesting project – the NIA IMPACT Collaboratory – where a primary goal is to fund a large group of pragmatic pilot studies to investigate promising interventions to improve health care and quality of life for people living with Alzheimer’s disease and related dementias. One of my roles on the project team is to ...
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Adding a “mixture” distribution to the simstudy package
I am contemplating adding a new distribution option to the package simstudy that would allow users to define a new variable as a mixture of previously defined (or already generated) variables. I think the easiest way to explain how to apply the new mixture option is to step through a few examples and see it in action. Specifying the “mixture�...
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Repeated measures can improve estimation when we only care about a single endpoint
I’ve been participating in the design of a new study that will evaluate interventions aimed at reducing both pain and opioid use for patients on dialysis. This study is likely to be somewhat complicated, involving multiple clusters, three interventions, a sequential and adaptive randomization scheme, and a composite binary outcome. I’m not go...
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A brief account (via simulation) of the ROC (and its AUC)
The ROC (receiver operating characteristic) curve visually depicts the ability of a measure or classification model to distinguish two groups. The area under the ROC (AUC), quantifies the extent of that ability. My goal here is to describe as simply as possible a process that serves as a foundation for the ROC, and to provide an interpretation of...
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