Presentation and handling of data, descriptive and inferential statistics

Abstract

The need for any doctor to comprehend, assimilate, analyse, and form an opinion on data cannot be overestimated. This chapter examines the presentation and handling of such data and its subsequent statistical analysis. It covers the organization and description of data, measures of central tendency such as mean, median, and mode, measures of dispersion (standard deviation), and the problems of missing data. Theoretical distributions, such as the Gaussian distribution, are examined and the possibility of data transformation discussed. Inferential statistics are used as a means of comparing groups, and the rationale and use of parametric and non-parametric tests and confidence intervals is outlined. The analysis of categorical variables using the chi-squared test and assessing the value of diagnostic tests using sensitivity, specificity, positive and negative predictive values, and a likelihood ratio are discussed. Measures of association are covered, namely linear regression, as is time-to-event analysis using the Kaplan–Meier method. Finally, the chapter discusses the statistical analysis used when comparing clinical measurements—the Bland and Altman method. Illustrative examples, relevant to the practice of anaesthesia, are used throughout and it is hoped that this will provide the reader with an outline of the methodologies employed and encourage further reading where necessary.

Feasibility, tolerance and effectiveness of enteral feeding in critically ill patients in prone position: More can be less with inappropriate analysis

“…different participants in each group). 3,4 However, Table 1 (as mentioned in reference 1) describes a single cohort ( n = 47), who in this study were exposed to two interventions: supine and prone positioning. However, analyses were performed on the assumption that there were two independent unpaired groups, effectively (and incorrectly) doubling the sample size.…”

“…Both the Student t- and the Mann-Whitney U- tests involve comparison of central tendency and spread, whilst the chi-squared test compares frequencies. 3,4 However, most results are presented as percentages, either of prescribed doses of nutrition, or of total cumulative time in the prone or supine position. The only result presented as mean ± standard deviation was gastric residual volume (5.3 ± 3.9 ml prone and 15.1 ± 18.5 ml supine).…”