Statistics

Effect Measure

Category archives for Statistics

[Previous installments: here, here, here, here, here, here] Last installment was the first examination of what “randomized” means in a randomized controlled trial (RCT). We finish up here by calling attention to what randomization does and doesn’t do and under what circumstances. The notion of probability here is the conventional frequentist one, since that’s how…

[Previous installments: here, here, here, here, here] After a detour through the meaning of causation and the need to find a substitute for what can’t, in principle, be observed (the counterfactual), we are now ready to consider what many of you might have thought would be the starting point, randomization. It’s a surprisingly difficult topic…

Just a day into the New Year I was feeling feisty and issued a challenge to readers and the Evidence Based Medicine (EBM) blogosphere in general. I asked for a critique of a fictitious uncontrolled, non-randomized non-blinded small scale clinical study. It was truly a fictitious study. I made it up. But I had a…

Thinking about confidence intervals

Like David Rind over at Evidence in Medicine I’m a consumer of statistics, not a statistician. However as an epidemiologist my viewpoint is sometimes a bit different from a clinician’s. As a pragmatic consumer, Rind resists being pegged as a frequentist or a Bayesian or any other dogmatic statistical school, which is wise. Let the…

Marilyn Mann pointed me to an interesting post by David Rind over at Evidence in Medicine (thanks!). It’s a follow-on to an earlier post of his about the importance of plausibility in interpreting medical literature, a subject that deserves a post of its own. In fact the piece at issue, “HIV Vaccines, p values, and…

Hate crimes, risks and numbers

I have been away (again) and out of internet contact most of the day, dealing with an unhappy family event. So this post is short but illustrates an important point that comes up frequently in epidemiology: the difference between risks and absolute numbers. The illustration is not medical, but I think sharper because of it:

Swine flu: How bad was the first wave?

One frequently hears claims that the current swine flu pandemic has been exaggerated because there are “only” 1000 or so deaths, while seasonal flu is estimated to contribute to tens of thousands of deaths a year. There are two reasons why this is not an apt comparison. We’ve discussed both here fairly often. The first…

Monday morning, start of week three of the official flu season (which began October 4). CDC’s scientific spokeswoman on the flu, Dr. Anne Schuchat has said we are seeing “unprecedented” flu activity for this time of year, including an unusual toll in the pediatric age group. What does “unprecedented” mean? It’s not very specific on…

When swine flu poked its head above water in the northern hemisphere in April our “normal” flu season was just ending. A surge of swine flu cases during a time when influenza was not usually seen was bewildering and confusing, not to mention alarming. We didn’t know what to expect nor were we sure if…

The other day we did something we don’t like to do when talking about flu, we made a prediction. We predicted a bad swine flu season in the fall in the northern hemisphere. The history of flu epidemiology is that making predictions is dangerous. Flu has the ability to make fools out of anyone, regardless…