ouR data generation

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 exploring ridge regression, Lasso regression, or other “regularization” methods. Alternatively, this can be used to very quickly generate correlated data (with one line of code) without going through the definition process. [Read More]

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 what kind of experiences, including interactions with the health care system, they have (and don’t have) before death. [Read More]

“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 could offer any tips to get me started with how I would do this? [Read More]

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 Wedge Trial. Unlike my previous work with stepped-wedge designs, where individuals were measured once in the course of the study, this study will collect patient outcomes from the home hospice care EHRs over time. [Read More]

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 innovative randomization scheme to ensure that two comparison groups were evenly balanced across important covariates. [Read More]

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 time depends only on the previous health status (in the immediate past). While there are packages to do this sort of thing (see for example the markovchain package), I hadn’t yet stumbled upon them while I was tackling my problem. [Read More]

Continuing a series of posts discussing the structure of intra-cluster correlations (ICC’s) in the context of a stepped-wedge trial, this latest edition is primarily interested in fitting Bayesian hierarchical models for more complex cases (though I do talk a bit more about the linear mixed effects models). The first two posts in the series focused on generating data to simulate various scenarios; the third post considered linear mixed effects and Bayesian hierarchical models to estimate ICC’s under the simplest scenario of constant between-period ICC’s. [Read More]

In the last two posts, I introduced the notion of time-varying intra-cluster correlations in the context of stepped-wedge study designs. (See here and here). Though I generated lots of data for those posts, I didn’t fit any models to see if I could recover the estimates and any underlying assumptions. That’s what I am doing now. My focus here is on the simplest case, where the ICC’s are constant over time and between time. [Read More]

In my last post, I wrote about within- and between-period intra-cluster correlations in the context of stepped-wedge cluster randomized study designs. These are quite important to understand when figuring out sample size requirements (and models for analysis, which I’ll be writing about soon.) Here, I’m extending the constant ICC assumption I presented last time around by introducing some complexity into the correlation structure. Much of the code I am using can be found in last week’s post, so if anything seems a little unclear, hop over here. [Read More]

A few weeks ago, I was at the annual meeting of the NIH Collaboratory, which is an innovative collection of collaboratory cores, demonstration projects, and NIH Institutes and Centers that is developing new models for implementing and supporting large-scale health services research. A study I am involved with - Primary Palliative Care for Emergency Medicine - is one of the demonstration projects in this collaboratory. The second day of this meeting included four panels devoted to the design and analysis of embedded pragmatic clinical trials, and focused on the challenges of conducting rigorous research in the real-world context of a health delivery system. [Read More]