= Solution
The source plot's sharp rise in the final year crosses the chosen control boundary. \b[Trigger a prompt independent investigation of the mortality signal.] First verify records, deaths, follow-up and expected-count calculations, then review <case mix>, changes in referral or recording, and plausible clinical explanations. The response should include appropriate clinical governance and safeguards while the cause is assessed; a statistical signal is not, by itself, proof of misconduct or a particular cause.
The stated null <average run length> of $111$ years makes a signal unusual under the calibrated null, while the alternative value of $5.2$ years indicates sensitivity to a sustained doubling under the specified model. Neither number gives the posterior probability that a doubling has occurred, and $1/111$ is not automatically the false-alarm probability for this particular ten-year history. Likewise the threshold is not a standalone fixed-test significance level.
The earlier value $X_{1993}=0$ says only that, at that point, no recent accumulated positive <log-likelihood ratio> survived the resets. It is \b[not evidence that the earlier death rate was certainly normal, and does not cancel the later signal]. The zero reset is deliberately part of the change-detection design; the 1994–1996 increments can independently justify an alarm. The full earlier clinical history remains relevant to investigation, even though a negative earlier accumulated score is not carried into the new <CUSUM> segment.
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