Cranberry juice may help lower BP but…

Cranberry juice may help lower BP but…

All you need to do is drink two 8 ounce glasses of cranberry juice per day for 8 weeks and your blood pressure will be statistically significantly lower. So states a randomized, blinded placebo-controlled trial presented at this year’s American Heart Association’s High Blood Pressure Research. According to the MedPage Today report, mean diastolic blood pressure fell by a whopping 3 mm Hg from baseline at the end of the study period. The difference was significant at the level of p = 0.049. Subjects given placebo showed no change in their average BP. Unfortunately, as appealing as this may sound, it’s another situation where statistical significance and clinical significance part ways. I have blogged about this before. What are the problems with cranberry juice study? The subjects were people of normal body mass index (average BMI, 28) who did not have hypertension. The mean fall in diastolic blood pressure was from 72 mm Hg to 69 mm Hg, both of which are in the normal range. A 3 mm Hg difference in diastolic blood pressure, even if it had occurred in a patient with hypertension, is not a clinically important difference. Systolic BP also fell by 3 mm Hg but the difference was not statistically significant, p = 0.12. A quote from the article states, “The trend didn’t meet traditional criteria for statistical significance, but the 89% odds of a systolic blood pressure reduction with the cranberry juice was still pretty good, [a study author] suggested.” Sorry, not only is that baloney, a 3 mm Hg difference in systolic BP is also not clinically important. A study from the Mayo Clinic found that when blood pressure is measured every 10 minutes throughout the day in healthy adults, both systolic and diastolic BPs varied as much as 8 to 10 mm Hg whether the subject was active or not. This indicates that a 3 mm Hg difference is very likely to have occurred by chance. Finally, the study was funded by Ocean Spray Cranberries and one of its employees was a co-author. You can drink cranberry juice if you like its taste, but don’t throw away the BP pills.

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1.) Write a paragraph summarizing what the article is saying about the difference between statistical and practical significance.