Blog Archives

A priori overfitting

The term overfitting usually describes fitting too complex a model to available data. But it is possible to overfit a model before there are any data. An experimental design, such as a clinical trial, proposes some model to describe the

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Probability of long runs

Suppose you’ve written a program that randomly assigns test subjects to one of two treatments, A or B, with equal probability. The researcher using your program calls you to tell you that your software is broken because it has assigned

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Volatility in adaptive randomization

Randomized clinical trials essentially flip a coin to assign patients to treatment arms. Outcome-adaptive randomization “bends” the coin to favor what appears to be the better treatment at the time each randomized assignment is made. The method aims to treat

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Personalized medicine

When I hear someone say “personalized medicine” I want to ask “as opposed to what?” All medicine is personalized. If you are in an emergency room with a broken leg and the person next to you is lapsing into a

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Posted in Clinical trials, Science, Statistics

How long will there be computer science departments?

The first computer scientists resided in math departments. When universities began to form computer science departments, there was some discussion over how long computer science departments would exist. Some thought that after a few years, computer science departments would have

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How do you justify that distribution?

Someone asked me yesterday how people justify probability distribution assumptions. Sometimes the most mystifying assumption is the first one: “Assume X is normally distributed …” Here are a few answers. Sometimes distribution assumptions are not justified. Sometimes distributions can be

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Small data

Big data is getting a lot of buzz lately, but small data is interesting too. In some ways it’s more interesting. Because of limit theorems, a lot of things become dull in the large that are more interesting in the

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Works well versus well understood

While I was looking up the Tukey quote in my earlier post, I ran another of his quotes: The test of a good procedure is how well it works, not how well it is understood. At some level, it’s hard

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A couple preprints

Here are a couple new preprints. Block-adaptive randomization. A proposed method for limiting the size of runs in a response-adaptive clinical trial. Skeptical and optimistic robust priors for clinical trials. Joint work with Jairo F├║quene and Luis Pericchi from University

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Why drugs often list headache as a side-effect

In an interview on Biotech Nation, Gary Cupit made an offhand remark about why so many drugs list headache as a possible side-effect: clinical trial participants are often asked to abstain from coffee during the trial. That also explains why

Posted in Clinical trials

Subtle variation on gaining weight to become taller

Back in March I wrote a blog post asking whether gaining weight makes you taller. Weight and height are clearly associated, and from that data alone one might speculate that gaining weight could make you taller. Of course causation is

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I promise I’m not trying to learn anything

Medical experiments come under greater scrutiny than ordinary medical practice. There are good reasons for such precautions, but this leads to a sort of paradox. As Frederick Mosteller observed We have a strange double standard now. As long as a

Posted in Clinical trials

Something like a random sequence but …

When people ask for a random sequence, they’re often disappointed with what they get. Random sequences clump more than most folks expect. For graphical applications, quasi-random sequence may be more appropriate.These sequences are “more random than random” in the sense

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Malaria on the prairie

My family loves the Little House on the Prairie books. We read them aloud to our three oldest children and we’re in the process of reading them with our fourth child. We just read the chapter describing when the entire

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Biostatistics software

The M. D. Anderson Cancer Center Department of Biostatistics has a software download site listing software developed by the department over many years. The home page of the download site allows you to see all products sorted by date or

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