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  "body": "\n## Summary\n\nThe sample mean and the sample covariance matrix summarise a sample of vectors by its centre and its spread.\nThey are the multivariate versions of the [[sample mean|03Y6AQ2S0J]] and the [[sample variance|0NHXGY2C5J]].\nThey are unbiased estimators of the mean vector and the [[covariance matrix|0V7G6WMFK0]], and they are the starting point of multivariate analysis.\n\n## Explanations\n\n### L1 human\n\nMeasure the height and the weight of each person in a group.\nThe sample mean is the average point: average height and average weight.\nThe sample covariance matrix records how much each quantity varies, and whether tall people tend to be heavy.\nFor the two points $(0, 0)$ and $(2, 2)$, the mean is $(1, 1)$, and both coordinates vary together, so the off-diagonal entry is positive.\n",
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