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Endoscopy 2016; 48(10): 899-908
DOI: 10.1055/s-0042-108727
Original article
© Georg Thieme Verlag KG Stuttgart · New York

Terminal digit preference biases polyp size measurements at endoscopy, computed tomographic colonography, and histopathology

Andrew A. Plumb
1   Centre for Medical Imaging, Division of Medicine, University College London, London, United Kingdom
,
Claire Nickerson
2   NHS Cancer Screening Programmes, Fulwood House, Sheffield, United Kingdom
,
Katherine Wooldrage
3   Cancer Screening and Prevention Research Group, Department of Surgery and Cancer, Imperial College London, London, United Kingdom
,
Paul Bassett
4   Research Support Centre, University College London, London, United Kingdom
,
Stuart A. Taylor
1   Centre for Medical Imaging, Division of Medicine, University College London, London, United Kingdom
,
Douglas Altman
5   Centre for Statistics in Medicine, University of Oxford, Oxford, United Kingdom
,
Wendy Atkin
3   Cancer Screening and Prevention Research Group, Department of Surgery and Cancer, Imperial College London, London, United Kingdom
,
Steve Halligan
1   Centre for Medical Imaging, Division of Medicine, University College London, London, United Kingdom
› Author Affiliations
Further Information

Publication History

submitted08 December 2015

accepted after revision26 April 2016

Publication Date:
21 July 2016 (online)

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Video Comment on Plumb et al.Endoscopy 2016; 48(10): v24-v24
DOI: 10.1055/s-0042-116909

Background and study aims: Terminal digit preference bias for “pleasing” numbers has been described in many areas of medicine. The aim of this study was to determine whether endoscopists, radiologists, and pathologists exhibit such bias when measuring colorectal polyp diameters.

Methods: Colorectal polyp diameters measured at endoscopy, computed tomographic colonography (CTC), and histopathology were collated from a colorectal cancer screening program and two parallel multicenter randomized trials. Smoothing models were fitted to the data to estimate the expected number of polyps at 1-mm increments, assuming no systematic measurement bias. The difference between the expected and observed numbers of polyps was calculated for each terminal digit using statistical modeling. The impact of measurement bias on per-patient detection rates of polyps ≥ 10 mm was estimated for each modality.

Results: A total of 92 124 individual polyps were measured by endoscopy (91 670 screening and 454 from trials), 2385 polyps were measured by CTC (1664 screening, 721 trials), and 79 272 were measured by histopathology (78 783 screening, 489 trials). Clustering of polyp diameter measurements at 5-mm intervals was demonstrated for all modalities, both in the screening program and the trials. The statistical models estimated that per-patient detection rates of polyps ≥ 10 mm were over-inflated by 2.4 % for endoscopy, 3.1 % for CTC, and 3.3 % for histopathology in the screening program, with similar trends in the randomized trials.

Conclusion: Endoscopists, radiologists, and pathologists all exhibit terminal digit preference when measuring colorectal polyps. This will bias trial data, referral rates for further testing, adenoma surveillance regimens, and comparisons between tests.

 

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