Show the data, don't conceal them

Abstract

Data presentation and statistical analysis in scientific writing are agreed to be in need of improvement, despite the profusion of advice and instruction. Recent evidence supports the need for better planning and analysis of animal experiments. This series of short articles aims to provide advice in small easily digested pieces, on a variety of topics, both basic and more specialized, that are relevant to readers of the journal. The present article encourages authors to present data clearly, preferably as a dot plot, so that the distribution of the values can be recognized. The use of different measures of distribution of a population, and different measures of precision of an estimate is contrasted.

Figure 1

Comparison of a dot plot with a plunger plot. A. two datasets, with the same mean value, displayed as either dot plots or plunger plots. The bars are mean values: error bars indicate SEM. B. subsamples of 6 data points from the above datasets. The line indicates the mean of these values.

Figure 2

Different types of error bar. In each pair of examples, 50 and 6 samples have been taken. The central line represents the mean value, and the error bars show the values stated. Note how the precision of the mean value (i.e. the SEM and the CI of the mean) is affected by the small sample, whereas the indices of dispersion (SD and CI of the population) are less affected.