Recommended: When the revolution came for Amy Cuddy

This is one of the best articles I have ever read in the popular press about the complexities of the research process.

This article by Susan Dominus covers some high profile research by Amy Cuddy. She and two co-authors found that your body language not only influences how others view you, but it influences how you view yourself. Striking a “power pose” meaning something like a “legs astride or feet up on a desk” can improve your sense of power and control and these subjective feelings are matched by physiological changes, Your testosterone goes up and your cortisol goes down. Both of these, apparently, are good things.

The research team publishes these findings in Psychological Science, a prominent journal in this field. The article receives a lot of press coverage. Dr. Cuddy becomes the public face of this research, most notably by garnering an invitation to give a TED talk and does a bang-up job. Her talk becomes the second most viewed TED talk of all time.

But there’s a problem. The results of the Psychological Science publication do not get replicated. One of the other two authors expresses doubt about the original research findings. Another research team reviews the data analysis and labels the work “p-hacking”.

It turns out that there is a movement in the research world to critically examine existing research findings and to see if the data truly supports the conclusions that have been made. Are the people leading this movement noble warriors for truth or are they shameless bullies who tear down peer-reviewed research in non-peer-reviewed blogs.

I vote for “noble warriors” but read the article and decide for yourself what you think. It’s a complicated area and every perspective has more than one side to it.

One of the noble warriors/shameless bullies is Andrew Gelman, a popular statistician and social scientist. He comments extensively about the New York Times article on his blog, which is also worth reading as well as many comments that others have made on his blog post. It’s also worth digging up some of his earlier commentary about Dr. Cuddy. Continue reading

PMean: 100 interview questions? A big oops on the very first one.

I shouldn’t do this, because we’ve all made mistakes, especially me. But I took a peek at a website with the intriguing title “100+ commonly asked data science interview questions” with the thought “Maybe I could be a data scientist”. But the author of this list choked on the very first question. It’s interesting to examining why the question is bad. Continue reading

Recommended: Search for unpublished data by systematic reviewers: an audit

The authors looked at all systematic reviews (excluding methodological reviews) published in a few key journals as well as a random sample of Cochrane reviews to see how often the authors tried to search for unpublised data. The answer is not often enough (64% or 130/203). The article also describes the success rate in getting unpublished data when the attempt was made (89% or 116/130) and how often authors found evidence of publication bias when they did such an assessment (40% or 27/68). Although some people have argued that it is not that important to search for unpublised data, this is still a big concern. A closely related article is Searching for unpublished data for Cochrane reviews: cross sectional study. Continue reading

PMean: What does large mean when talking about negative values?

Dear Professor Mean, I saw a paper where the authors said that they wanted a diagnostic test with a large negative likelihood ratio, because it was important to rule out a condition. False negatives mean leaving a high risk condition untreated. But don’t they mean that they want a diagnostic test with a small likelihood ratio?

Okay, I agree with you, but it’s an understandable mistake. Let’s quickly review the idea of likelihood ratios. A positive likelihood ratio is defined at Sn / (1-Sp) where Sn is the sensitivity of the diagnostic test and Sp is the specificity. For a diagnostic test with a very high specificity, you get a very large ratio, because you are putting a really small value in the denominator. For Sp=0.99, for example, you would end up getting a positive likelihood ratio of 50 or more (assuming that Sn is at least 0.5).

The positive likelihood ratio is a measure of how much the odds of disease are increased if the diagnostic test is positive.

A negative likelihood ratio is defined as as (1-Sn) / Sp. For a diagnostic test with a very large sensitivity, the negative likelihood ratio is very close to zero. For Sn=0.99, the likelihood ratio is going to be 0.02 or smaller, assuming that Sp is at least 0.5.

The negative likelihood ratio is a measure of how much the odds of disease are decreased if the diagnostic test is negative.

The two likelihood ratios should remind you of the acronyms SpIn and SnOut. SpIn means that if specificity is large, then a positive diagnostic test is good at ruling in the disease. This isn’t always the case, sadly, and for many diagnostic tests, the next step after a positive test is not to treat the disease, but to double check things using a more expensive or more invasive test.

SnNout means that if the sensitivity is large, then a negative diagnostic test is good at ruling out the disease. You can safely send the patient home in some settings, or start looking for other diseases in different settings.

That sounds great, but sometimes you are very concerned about false negatives, and you don’t want to send someone home if they actually have the disease. If you are worried about a cervical fracture, ruling out the fracture and sending someone home might lead to paralysis or death if you have a false negative. So you want to be very sure of yourself in this setting.

Now with regard to the comment above, I think it is just a case of careless language. When the authors say “large negative likelihood ratio”, they should have said “extreme negative likelihood ratio” meaning a likelihood ratio much much smaller than one. I’ve done it myself when I talk about a correlation of -0.8 as being a “big” correlation because it is very far away from zero.

We tend to shy away from words like “small” when we talk about a negative likelihood ratio being much less than 1, because “small” in some people’s minds means “inconsequential” when the opposite is true. When I am careful in my language, I try to use the word “extreme” to mean very far away from the null value (1 for a likelihood ratio or 0 for a correlation) rather than “large” or “small”.

Recommended: OpenRefine: A free, open source, powerful tool for working with messy data

I have not had a chance to use this, but it comes highly recommended. OpenRefine is a program that uses a graphical user interface to clean up messy data, but it saves all the clean up steps to insure that your work is well documented and reproducible. I listed Martin Magdinier as the “author” in the citation below because he has posted most of the blog entries about OpenRefine, but there are many contributors to this package and website. Continue reading

Recommended: How to increase value and reduce waste when research priorities are set

This is the first in a series of articles on reducing waste in research. It focuses on funding agencies and recommends that funders should support more work on making research replicable, be more transparent on how they set priorities, make sure that research proposals are justified through a systematic review of previous research, and encourage greater openness of research in progress to encourage collagoration. Other articles in this series cover research design, conduct, and analysis, regulation and management, inaccessible research, and incomplete reports of research. Continue reading

Recommended: Randomized Controlled Trials in Health Insurance Systems

While researchers often use data from health insurance systems to conduct observational studies, the authors of this research paper point out that you can also conduct randomized trials as well. You can randomly assign different levels of insurance coverage and then get claims data to evaluate how much difference there is, if any, in the levels of coverage. This approach is attractive because you do not need a lot of resources, and you can very quickly get a very large sample size. Since insurance data is collected for administrative needs rather than research needs, you have to contend with inaccurate or incomplete data, potentially causing loss of statistical efficiency or producing biased results. The authors offer some interesting examples of actual studies, propose new potential studies, and offer general guidance on how to conduct a randomized trial from health insurance systems. Continue reading

Recommended: Announcing a new monthly feature: What’s going on in this graph

Through the effort of a team of statisticians with the American Statistical Association, the New York Times is producing a new resource for educators called “What’s Going On in This Graph?”. This is similar to another New York Times effort called “What’s Going On in This Picture?”

Every month the New York Times will publish a graph stripped of some key information and ask three questions: What do you notice? What do you wonder? and What do you think is going on in this graph?

The content will be suitable for middle school and high school students, but I suspect that even college students will find the exercise interesting.

The first graph will appear on September 19 and on the second Tuesday of every month afterwards. Continue reading