Use of stacked proportional bar graphs (“Grotta bars”) to visualize functional outcome distributions in observational neurology research

Abstract

AbstractBackground and ObjectivesStacked proportional bar graphs (nicknamed “Grotta bars”) are commonly used to visualize functional outcome scales in stroke research and are also used in other domains of neurological research. In observational studies that present adjusted effect estimates, Grotta bars can mislead readers if they show unadjusted, confounded comparisons. In a sample of recent observational neurology studies with confounding-adjusted effect estimates, we aimed to determine the frequency with which Grotta bars were used to visualize functional outcomes and how often unadjusted Grotta bars were presented without an accompanying adjusted version. We also assessed the methods used to generate adjusted Grotta bars.MethodsIn this meta-research study, we systematically examined all observational studies published in the top 15 Clinical Neurology journals between 2020-2021 with an ordinal functional outcome and confounding-adjusted effect estimate. We determined whether at least one comparison using Grotta bars was present, whether the visualized comparisons were adjusted, and which adjustment strategies were applied to generate these graphs.Results250 studies met all inclusion criteria. Of these, 93 (37.2%) used Grotta bars to depict functional outcome scale distributions, with 73 (81.7%) presenting only Grotta bars without model-based adjustment. Amongst the 17 studies that presented Grotta bars adjusted using a model, the adjustment strategies included propensity score matching (n=10; 58.8%), regression (n=6; 35.3%), and inverse probability weighting (n=1; 5.9%). Most studies with Grotta bars (n=87; 87.9%) were stroke studies.DiscussionGrotta bars were most often used in stroke research within our sample. Papers that present adjusted associations for functional outcomes commonly showed only unadjusted Grotta bars, which alone may be misleading for causal questions. In observational research, Grotta bars are most informative if an adjusted version, aligning with adjusted effect estimates, is presented directly alongside the unadjusted version. Based on our findings, we offer recommendations to help authors generate informative Grotta bars and facilitate correct interpretation for readers.