How can light travel more than 13.7 billion light-years in 13.7 billion years?
William B. Keith
THE EDITORS REPLY: Space is expanding, carrying objects such as galaxies and photons with it, so light travels a greater distance than a simple calculation (such as speed multiplied by time) might suggest. An object that emitted light 13.7 billion years ago is now 42 billion light-years away. This figure depends on the values of cosmological parameters.
As a biostatistician, I concur with Charles Seife’s critical comments about the abuses of the so-called p-value as a measure of statistical significance of data in “The Mind-Reading Salmon” [Advances]. Statisticians have criticized this methodology before, sometimes even recommending banning it. I would temper such criticism, however, by pointing out that there are a variety of adjustments to p-values to take into account the kind of multiple-testing artifact Seife refers to, and they are often used (though perhaps not as much as they should be).
Another issue relevant to this topic is the publication bias of many journals, which often give greater weight toward publishing articles that report statistically significant findings over those that don’t. I have advocated before that one way to mitigate problems with null-hypothesis significance testing is for editors of scientific journals to employ “results blind” decision making in determining whether to publish and make it be known that they are doing so. Articles should be accepted for publication based primarily on the judged importance and relevance of the reported study, which is usually stated and defended in the “introduction” section of the manuscript, and whether the methodology (including that of the data analysis) is sound, which can be assessed via the “methods” section of the manuscript.
With this kind of review process, if 20 studies of the effectiveness of a truly ineffective drug are conducted, and one of them shows a significant effect with a p-value of 0.05 because of chance alone, investigators for the other 19 studies not showing any effect would presumably not be inhibited from writing up and submitting reports of these for publication out of fear that they’ll be denied publication because of their nonsignificant results. Publishing of those results would then cause the scientific audience to be rightly skeptical of the one significant finding amid the many reports not demonstrating it.
Joseph J. Locascio
Instructor in Neurology
Harvard Medical School