Cite this post as:
Rory Spiegel. EMNerd – More on the FELLOW Trial. EMCrit Blog. Published on November 28, 2015. Accessed on December 7th 2021. Available at [https://emcrit.org/emcrit/fellow-trial-methodology/ ].
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Unless otherwise noted at the top of the post, the speaker(s) and related parties have no relevant financial disclosures.
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Awesome stuff Rory! I think your summary really helps make clear that this trial doesn’t truly answer the question of whether apneic oxygenation really works or not. It’s hard to frame it as one that does, given that only 30% of patients were truly apneic. I’d like to see a trial that truly randomizes ApOx vs none, with a standard method of PreOx for all comers. What sample size would be needed? Until then, it makes sense to keep on with an intervention that makes a lot of physiological sense with no known harms, no appreciable cost, and one that’s… Read more »
Love the critical thinking and breakdown of the trial – thanks for the time and effort. I am concerned that the loss of power due to nonparametric hypothesis testing is a bit overstated. Nonparametric tests are, by nature, more conservative – given our fear of type I error, this is a benefit. As you said, it comes at the cost of decreasing power. However, that decrease in power is not constant; usually for trials greater than 100 participants, the decreased power is negligible. Especially since all results were non-significant, I would not consider the choice of appropriate statistical test a… Read more »
HI William, Thank you so much for the kind words. I think your points on non-parametric testing are entirely valid. My intention of the post was to discuss the fact that this trial was incapable of differentiating a clinically important difference from statistical chance. Choosing a continuous variable of questionable clinical significance as their primary outcome, likely was far more of a factor in why the study was underpowered than their use of a non-parametric analysis but I thought it was important to discuss both factors in the analysis. To your second point, from my perspective the goal of apneic… Read more »
The unpinning philosophy of the P value is that the null hypothesis is correct. Therefore, I think that your opening statement is incorrect. This is explained in 1 and 2. It is also tempting to look for absolute differences that are non-significant then explain that the study is underpowered. The reader is then left with the impression that had the study been bigger then the differences would become significant. This is also incorrect and explained in 3. 1. Goodman SN. Towards evidence based medical statistics. The P value fallacy. Ann Intern Med 1999;130:995-1004. 2. Sedgwick P. Understanding P values. BMJ… Read more »
Hi Richard, Thank you so much for your response. While I completely agree with your statement, “the unpinning philosophy of the p-value is that the null hypothesis is true”, I don’t think a failure to reject the null hypothesis proves the null hypothesis. Rather it states the data was unable to demonstrate a difference. Goodman discusses this misconception in (1). Yes I agree any retrospective power analysis in a negative trial will invariably demonstrate an underpowered trial. Rather using a confidence interval approach to determine whether a trial is capable of differentiating a clinically important outcome from statistical chance is… Read more »