EXHIBIT 2 Catehing a Breath Stopping Sleep Apnea Title: Statistical versus Clini

Question

EXHIBIT 2 Catehing a Breath Stopping Sleep Apnea Title: Statistical versus Clinical Significance: They Are Not the Same Author: The Skeptical Scalpel Source: Skeptical Scalpel, August 8, 2011, http://skepticalscalpel. blogspot.com/2011/08/ statistical-vs-clinical-significance.html In reference to an article that appeared on MedPage Today, August 5th, 2011 ("Compression Stocking Help Sleep Apnea," by Michael Smith), the Skeptical Scalpel writes: MedPage Today featured an article about the beneficial effects of daytime wearing of compression stockings on obstructive sleep apnea. The premise was that i caused by fluid coming from the legs when patients were in the supine position at night. Twelve patients who served as their own controls wore compression stockings for a week and then no stockings for a week alternating. The stockings lowered the amount of fluid in the neclk a statistically significant difference. So far, so good. increased edema in the neck could be by 60%, This resulted in another highly statistically significant finding, which was a 36% reduction in episodes of apnea (cessation of breathingl and hypopnea [inadequate breathingl. Sounds good, right? The problem is that the average number of episodes of apnea/hypopnea decreased from 48 per hour to 31 per hour. Patients experiencing more than 30 episodes of apnea/hypopnea per hour are classified as having severe obstructive sleep apnea. This means that the treatment only put the patients in the low range of severe obstructive sleep apnea. They still would require maximum therapy. Is a reduction in apnea/hypopnea episodes that does not move the patient out of the severe category really clinically significant? It does not seem so to me. Questions Clearly identify what the null (H,) and alternative (H,) hypotheses appear to be in the context of this article. Which one was chosen and why? 1. The Skeptical Scalpel is making a point about practical significance. What is that point? Do you agree? 2.

Explanation / Answer

Solution

Part (a)

Besides the point that a reduction of 60% and 36% are not only statistically significant, the counter-point made out in the critique article that a rate of 31episodes per hour is still higher than the threshold rate of 30 episode per hour and hence the study results are not practically significant is NOT tenable because that rate is based on a very small sample of size 12. In view of this grave overlook, the real hypotheses to be tested are:

Null H0: population rate is 0.3 vs Alternative: H0: population rate is less than 0.3.

If this hypothesis is tested with a sample size of 12 and rejected, there is enough evidence to suggest that point made out in the critique article in NOT TENABLE. ANSWER

Part (b)

As already explained above, the argument of the critique article is debatable.

However, the question of statistical significance and practical significance is a very valid and also relevant point which needs utmost attention in scientific research.

A striking example would be: a correlation coefficient of 0.2 may turn out to be statistically significant, but it is NOT practically significant at all because a correlation coefficient, r of 0.2 implies that the r2 is 0.04 which means that the predictor variable is able to account for only 4% of the variation in the response variable rendering it a very poor predictor. ANSWER

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