Page 82 - Ultrasonography in Prehospital and Emergency Medicine - Rein Ketelaars

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Chapter 3
ly blinded researcher recorded the elapsed time (s), the observer’s diagnosis and perceived image quality rated on a 1–5 Likert scale (1, very poor; 5, very good). For every observer, their experience (years) with lung US and preferred transducer type for lung US was recorded.
Statistical analysis
Normally distributed data are reported as mean and standard deviation (SD). Data with an asymmetrical distribution are reported as median and interquartile range (IQR). We calculated the difference in elapsed time and image quality between transducers in every patient and observer: linear-array vs curved-array; linear-array vs phased-array; curved-ar- ray vs phased-array. Then, we fitted a linear mixed model with a random intercept to these differences to account for clustering within each observer. A two-tailed McNemar’s test for clustered data (Durkalski’s Chi-square test) was used to test for differences between the transducers in diagnostic performance. The Wilcoxon signed-rank test was used to test for differences in time until final diagnosis between diagnoses (normal ventilation and pneumo- thorax). For all statistical tests, significance level was set to .05. For statistical analysis, IBM SPSS Statistics for Windows, version 25.0 (IBM Corp., Armonk, NY, USA) and R, version 3.4.1, lme4 package installed (R Foundation for Statistical Computing, Vienna, Austria) were used.