Stats Made Easy

“Too little attention has been paid to the statistical challenges in estimating small effects.”

  — Andrew Gelman and David Weakliem, “Of Beauty, Sex and Power,” American Scientist, Volume 97, July-August 2009 .

In last week’s “In the Lab” column of the Wall Street Journal (WSJ)*, Sarah Rubinstein reported an intriguing study by the “light and health” program of the Rensselaer Polytechnic Institute (RPI).  The director, Mariana Figueiro, is trying to establish a lighting scheme for older people that will facilitate their natural rhythms of wakefulness and sleep.  In one 2002 experiment (according to WSJ), Dr. Figueiro subjected four Alzheimer patients to two hours of blue, red or no light-emitting diodes (LEDs).  After then putting the individuals to bed, their nurses made observations every two hours and found that the “blue-light special” out-did the red by 66% versus 54% on how often they caught patients napping.

Over the years we’ve accumulated many electrical devices in our bedroom – television, cable box, clocks, smoke and carbon monoxide monitors, etc., which all feature red lights.  They don’t bother me, but they keep my wife awake.  So it would be interesting, I think, if blues would promote snooze.  Unfortunately the WSJ report does not provide confidence intervals on the two percentages – nor do they detail the sample size so one could determine statistical significance on the difference of 0.12 (0.66 minus 0.54).  (I assume that each of the 4 subjects were repeatedly tested some number of times.)  According to this simple calculator posted by the Southwest Oncology Group (a national clinical research group), it would take a sample size of 554 to provide 80% power for achieving statistical significance at 0.05 for this difference!

So, although whether blue light really does facilitate sleep remains questionable, I am comforted by the testimonial of one of the study participants (a 100 years old!) – “It’s a beautiful light,” she says.

PS. Fyi, for more sophisticated multifactor experimentation (such as for screening studies), Stat-Ease posted a power calculator for binomial responses and provided explanation in its June 2009 Stat-Teaser newsletter .

* “Seeking a Light Approach to Elderly Sleep Troubles,” p. D2, 7/7/09