Reducing the length of mechanical ventilation with significance: a case study of sample size estimation trial design using Monte-Carlo simulation

Yeong Shiong Chiew, Christopher Pretty, Elena Moltchanova, Carl Scarrott, Daniel Redmond, Geoffrey M. Shaw, J. Geoffrey Chase

Research output: Chapter in Book/Report/Conference proceedingConference PaperOther

3 Citations (Scopus)


The power of a study can be established with estimation of total effective sample size (Ntotal). In this study, the impact of the length of mechanical ventilation (LoMV) distribution shape in intensive care on the estimated Ntotal is investigated. This study provides an overview on the study design involving LoMV, the resulting potential limitations, and the criteria for a 'successful' design. Data from mechanical ventilated patients in a single-center intensive care unit were used in this study. The Ntotal was estimated using two methods: 1) Model-based Altman's nomogram (a standard); and 2) Monte-Carlo simulation. Using Monte-Carlo simulation, a patient selection criteria is imposed to estimate Ntotal from 'realistic' patient cohorts. The Altman nomogram shows that the Ntotal to detect a 25% change in LoMV (ΔLoMV) at power of 0.8 is ≥1000 patients. For the Monte-Carlo simulation, a Ntotal ≥260 patients is needed to detect similar changes. It is important to consider the LoMV distribution shape and variability, particularly relative to target patient groups who might benefit from the intervention. Assessment of ΔLoMV in response to treatment should be carefully considered to avoid an under-powered studies. The Monte-Carlo simulation combined with objective patient selection provides better design of such studies.

Original languageEnglish
Title of host publication9th IFAC Symposium on Biological and Medical Systems BMS 2015
Number of pages6
Publication statusPublished - 1 Sept 2015
Externally publishedYes
EventIFAC Symposium on Biological and Medical Systems 2015 - Berlin, Germany
Duration: 31 Aug 20152 Sept 2015
Conference number: 9th


ConferenceIFAC Symposium on Biological and Medical Systems 2015
Abbreviated titleBMS 2015


  • Length of mechanical ventilation
  • Outcome
  • Power analysis
  • Sample size

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