Summarize, visualize, and understand data before diving into inference.
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Variance measures average squared deviation from the mean. Standard deviation has the same units as the data — it's the most widely used spread measure. These connect to the normal distribution via the 68-95-99.7 rule.
Mean = 40/5 = 8
Deviations: −4, −1, 0, 2, 3. Squared: 16, 1, 0, 4, 9
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Skewness describes asymmetry: right-skewed (mean > median, long right tail), left-skewed (mean < median). Kurtosis describes tail heaviness. The normal distribution has skewness 0 and kurtosis 3 (by convention, "excess kurtosis" = 0).
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