Statistics & Standard Deviation

What standard deviation actually measures

Standard deviation describes how spread out values are around the mean. A small standard deviation means data points cluster close to average; a large one means they're spread widely — even if two datasets share exactly the same mean.

Population vs. sample — the detail that changes your answer

If your data is the entire population, divide by n. If it's a sample meant to estimate a larger population, divide by n − 1 (Bessel's correction). Using the wrong one produces a systematically biased result, especially noticeable with small datasets.