Following are many patients diastolic blood pressure mm Hg f

Following are many patients\' diastolic blood pressure (mm Hg) figures. Their standard deviation is about 6.

81, 91, 81, 75, 72, 76, 84, 90, 95, 77, 79, 86, 71, 75, 89, 85, 80, 77, 74, 80, 79, 82, 90, 83, 81, 72, 82, 78, 80

If you were to add 9 to all of these values, what would be the new standard deviation? You should just estimate and enter the closest whole number.

Solution

New standard deviation will still be about 6

The reason is that when every number is increased by 9, the sample mean also increases by 9. Thus, the deviations from sample mean, di\'s, remain the same as previous case, leading to same squared sum of deviation, same variance and thus same standard deviation.