64 items | 7 visits
Clever research tricks and general info
Updated on Jan 19, 17
Created on Sep 26, 13
Category: Health & Wellness
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Functional MRI (fMRI) is 25 years old, yet surprisingly its most common statistical methods have not been validated using real data. Here, we used resting-state fMRI data from 499 healthy controls to conduct 3 million task group analyses. Using this null data with different experimental designs, we estimate the incidence of significant results. In theory, we should find 5% false positives (for a significance threshold of 5%), but instead we found that the most common software packages for fMRI analysis (SPM, FSL, AFNI) can result in false-positive rates of up to 70%. These results question the validity of some 40,000 fMRI studies and may have a large impact on the interpretation of neuroimaging results.
I’m not a big fan of the whole false-positive, false-negative thing. In this particular case it makes sense because they’re actually working with null data, but ultimately what you’ll want to know is what’s happening to the estimates in the more realistic case that there are nonzero differences amidst the noise. The general message is clear, though: don’t trust FMRI p-values. And let me also point out that this is yet another case of a classical (non-Bayesian) method that is fatally assumption-based.
Perhaps what’s the most disturbing thing about this study is how unsurprising it all is. In one sense, it’s big big news: FMRI is a big part of science nowadays, and if it’s all being done wrong, that’s a problem. But, from another perspective, it’s no surprise at all: we’ve been hearing about “voodoo correlations” in FMRI for nearly a decade now, and I didn’t get much sense that the practitioners of this sort of study were doing much of anything to clean up their act. I pretty much don’t believe FMRI studies on the first try, any more than I believe “gay gene” studies or various other headline-of-the-week auto-science results.
Dr Eklund now used the current analysis methods and compared 20 healthy people with 20 other healthy people. In other words, there should not have been any differences -- or, in any case only the five percent that chance provides. In total he made three million comparisons of randomly selected groups with data from 499 healthy persons.
"The differences were considerably greater than five percent, up to 60 percent in the worst case," Dr Eklund says.
This means that the analyses could have shown positive results where there shouldn't have been any, thereby indicating brain activity where there was no activity.
He also analysed the same data set with his more calculation-heavy method and obtained a considerably better correspondence, with differences in the expected five percent of cases.
In 2012, Amgen researchers made headlines when they declared that they had been unable to reproduce the findings in 47 of 53 'landmark' cancer papers1. Those papers were never identified
The stem-cell field holds enormous promise for therapy. As a result, all claims of considerable importance should be verified with utmost care before being made public. The Review suggests that such claims in the field of reprogramming and pluripotency should be demonstrated in more than one experimental model, and encourages their independent replication.
Nature will endeavour to help the field to achieve its promise, and is looking at ways to support and encourage this reproducibility enterprise. For example, we ask authors to include more details about the methods developed in their studies. We strongly encourage our authors to deposit step-by-step protocols on freely accessible platforms, such as Protocol Exchange (www.nature.com/protocolexchange) — this may be requested for extraordinary claims, at the editor’s discretion. We encourage our authors to verify the origin of the cell lines they use, as we do for cancer cell lines (see Nature 520, 264; 2015).
The Review concludes: “Science is ultimately a self-correcting process where the scientific community plays a crucial and collective role.” In this case, the stem-cell community has excelled in that role and should be congratulated.
64 items | 7 visits
Clever research tricks and general info
Updated on Jan 19, 17
Created on Sep 26, 13
Category: Health & Wellness
URL: