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Confounding explains ‘deaths avoided’
  1. Johan Michael van Schalkwyk
  1. Correspondence to Dr Johan Michael van Schalkwyk, Auckland City Hospital—Anaesthesia and Perioperative Medicine, 2 Park Road Grafton, Auckland 1023, New Zealand; johanvs{at}adhb.govt.nz

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Although it is clear that in the UK, standardised mortality rates have decreased dramatically over the past three decades,1 it may not be immediately apparent that this secular trend may substantially confound relatively short-term studies. Based on retrospectively obtained, uncontrolled data, Schmidt et al2 assert that introduction of an electronic physiological surveillance system reduced excess deaths. If, however, we control for the secular decrease in mortality rate, then this apparent benefit almost vanishes, as is shown in table 1, where I have applied the relevant decrease in standardised mortality rate for …

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