Clinical Trials

Clinical Trials: A Practical Guide ■❚❙❘Table 2. Summary of graphs used to display categorical and continuous data.Graph Features Categorical data Numeric dataBar chart • Frequency proportional to length of bar Yes No• Visually very strong, easy to interpret• Bars separated by gaps to indicate discrete dataPie chart • Percentages represent square of frequency Yes No• Differences between groups over-represented• Less informative than bar chartsDot plot • Each observation represented by a dot No Yes• Continuous data tend to be grouped• Can be used to display median value and IQRStem and leaf plot • Each digit in a leaf represents a data point No Yes• Looks similar to a rotated histogram• Very easy to draw by hand if there are smallamounts of dataBox plot • Displays skew of data No Yes• Illustrates median, IQR, and range• Truncated box plot used to spot outliersHistogram • Continuous data usually displayed in categories No Yesof equal width• Bars do not have spaces between them• Area of bar is proportional to frequencyScatter plot • Displays relationship between two continuous No Yesvariables, x and y, using a regression line• Influential points can mislead interpretation of lineLine graph • All consecutive data are connected by a line No Yes• Can be used to depict fluctuating trends,median, and mean.• Overlaid line graphs can create a spaghetti plotForest plot • Used to display point estimates and their Yes Yesconfidence intervals for multiple groups• In meta-analyses, a diamond at the base of thegraph represents the pooled intervention effect• Allows visual assessment of heterogeneitybetween groupsFunnel plot • Used to compare treatment effects of individual Yes Yesstudies in a meta-analysis• Plots study precision against correspondingtreatment effect• Good for examining publication bias, but notfully robustGraphs for • Mosaic displays represent multiway Yes Yesthree variablescontingency tables• Icons supplement bar charts and pie charts,particularly with small sample size• Surface plots display quantitative datain three dimensionsIQR = interquartile range.423