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  "body": "\n## Summary\n\nThe observed information is minus the second derivative of the log-likelihood of the data actually observed.\nIt is usually evaluated at the [[maximum likelihood estimate|0FREPFKNS7]].\nIt is a data-based counterpart of the [[Fisher information|G1Z3WSTE8Q]], whose expected value it equals under regularity conditions.\nIt gives standard errors for maximum likelihood estimates.\n\n## Explanations\n\n### L1 human\n\nDraw the log-likelihood as a curve with a peak at the best estimate.\nThe observed information is the curvature at that peak.\nA sharp peak means the data strongly favour a narrow range of values, so the estimate is precise.\nFor example, with Poisson counts of total $t$ in $n$ observations, the observed information at the estimate $t/n$ is $n^2/t$.\n",
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