The increasing use of ordinal variables in different fields has led to the introduction of new statistical methods for their analysis. The performance of these methods needs to be investigated under a number of experimental conditions. Procedures to simulate from ordinal variables are then required. In this article, we deal with simulation from multivariate ordinal random variables. We propose a new procedure for generating samples from ordinal random variables with a prespecified correlation matrix and marginal distributions. Its features are examined and compared with those of its main competitors. A software implementation in R is also provided along with examples of its application.

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Generating correlated Poisson random variables is fundamental in many applications in the management and engineering fields, and in many others where multivariate count data arise. Multivariate Poisson data are often approximately simulated by either independent univariate Poisson or multivariate Normal data, whose implementation is provided by the most common statistical software packages such as R. However, such simulated data are often not satisfactory. Alternatively, methods for simulating multivariate Poisson data can be used, but they are adversely affected by limitations ranging from computational complexity to restrictions on the correlation matrix, which dramatically reduce their practical applicability. In this work, we propose a new method that is highly accurate and computationally efficient and can be usefully employed even by non‐expert users in generating correlated Poisson data (and, more generally, any discrete variable), with assigned marginal distributions and correlation matrix. Copyright © 2014 John Wiley & Sons, Ltd.

BackgroundICU patients must be kept conscious, calm, and cooperative even during the critical phases of illness. Enteral administration of sedative drugs might avoid over sedation, and would be as adequate as intravenous administration in patients who are awake, with fewer side effects and lower costs. This study compares two sedation strategies, for early achievement and maintenance of the target light sedation.MethodsThis was a multicenter, single-blind, randomized and controlled trial carried out in 12 Italian ICUs, involving patients with expected mechanical ventilation duration > 72 h at ICU admission and predicted mortality > 12% (Simplified Acute Physiology Score II > 32 points) during the first 24 h on ICU. Patients were randomly assigned to receive intravenous (midazolam, propofol) or enteral (hydroxyzine, lorazepam, and melatonin) sedation. The primary outcome was percentage of work shifts with the patient having an observed Richmond Agitation-Sedation Scale (RASS) = target RASS ±1. Secondary outcomes were feasibility, delirium-free and coma-free days, costs of drugs, length of ICU and hospital stay, and ICU, hospital, and one-year mortality.ResultsThere were 348 patients enrolled. There were no differences in the primary outcome: enteral 89.8% (74.1–100), intravenous 94.4% (78–100), p = 0.20. Enteral-treated patients had more protocol violations: n = 81 (46.6%) vs 7 (4.2%), p < 0.01; more self-extubations: n = 14 (8.1%) vs 4 (2.4%), p = 0.03; a lighter sedative target (RASS = 0): 93% (71–100) vs 83% (61–100), p < 0.01; and lower total drug costs: 2.39 (0.75–9.78) vs 4.15 (1.20–20.19) €/day with mechanical ventilation (p = 0.01).ConclusionsAlthough enteral sedation of critically ill patients is cheaper and permits a lighter sedation target, it is not superior to intravenous sedation for reaching the RASS target.Trial registrationClinicalTrials.gov, NCT01360346. Registered on 25 March 2011.Electronic supplementary materialThe online version of this article (10.1186/s13054-018-2280-x) contains supplementary material, which is available to authorized users.

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