Clinical Trials

❘❙❚■ Chapter 36 | Use of FiguresFunnel plotsA funnel plot can also be used to compare the treatment effects of individualstudies in a meta-analysis. It is essentially a plot of the study precision againstthe corresponding treatment effect (see Chapter 38 for more). Funnel plots aregood for examining publication bias [7], but are not fully robust. In a reviewof 198 published meta-analyses, the shape of the funnel was determined by anarbitrary choice of the method to construct the plot. When different definitions ofprecision and/or effect measure were used, the conclusion about the shape of thefunnel changed in 86% of cases [8].Graphs for three variablesOther, less common, graphs that are used to display three dimensions includemosaic displays, icons, and surface plots. In brief, a mosaic display uses thestrengths of a bar chart to represent multiway contingency tables [9]. Icons area potential supplement to bar charts or pie charts, particularly when the samplesize is small [10]. Surface plots are useful for displaying quantitative data in threedimensions, ie, there are x, y, and z axes for plotting points and the graph must beprinted in a three dimensional representation [11].ConclusionGraphical representation facilitates the evaluation and comparison of outcomevariables among different groups, and enables an appropriate choice of statisticalmethods. In this chapter, we have explored a variety of graphs that are commonlyused in clinical reports (see Table 2 for a summary). The choice of graph isdetermined by the purpose of the exercise and the type of data to present. In atrial report, all of the graphs should be appropriately labeled and containsufficient information without needing to refer back to the text. Sometimes morethan one graph is required, giving importance to simplicity.References1. Petrie A, Sabin C. Medical Statistics at a Glance. Oxford: Blackwell Publishing, 2000.2. Kirkwood BR, Sterne JAC. Essential Medical Statistics. Oxford: Blackwell Publishing, 2003.3. Norleans MX. Statistical Methods for Clinical Trials. New York: Marcel Dekker, 2000.4. Dragsted UB, Gerstoft J, Pedersen C, et al. Randomized trial to evaluate indinavir/ritonavirversus saquinavir/ritonavir in human immunodeficiency virus type 1-infected patients:the MaxCmin 1trial. J Infect Dis 2003;188:635–42.5. Alderson P, Roberts I. Corticosteroids in acute traumatic brain injury: systematic reviewof randomised controlled trials. BMJ 1997;314:1855–9.424