Two classes have the same average marks — how can statistics show they're actually very different?
Compare their spread using standard deviation.
Compare their spread using standard deviation. Two data sets can share a mean yet differ wildly in how the values scatter around it. A small standard deviation means the marks are tightly clustered near the average (consistent performance); a large one means they're spread out with high and low extremes (uneven performance). So the mean tells you the centre, but the standard deviation reveals the consistency — essential for really comparing the two classes.
Key point
Standard deviation measures spread around the mean; equal means can hide very different spreads.
Common mistake
assuming equal averages mean the two groups are alike.
Memory tip
mean = centre, standard deviation = spread — you need both to compare.
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