In a survey, systolic blood pressure has a sample standard deviation of 15 mmHg in a sample of 100 subjects. The quantity 15 divided by the square root of 100 equals 1.5 mmHg. This value represents:

• A The standard deviation of individual blood pressures in the population
• B The probability that the sample mean equals the population mean
• C The range of individual values around the median
• D The standard deviation of the sampling distribution of the sample mean ✓

Explanation

Dividing the sample standard deviation by the square root of n yields the standard error of the mean, which describes how much sample means fluctuate from sample to sample around the population mean. It measures precision of the estimated mean, not scatter of individual observations, which is described by the standard deviation itself. Because it shrinks with increasing n, larger samples give more stable estimates of the mean.

Reference: Mahajan's Methods in Biostatistics for Medical Students and Research Workers, 9th ed.

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