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Radiologists and Clinical Trials: Part 2: Practical Statistical Methods for Understanding and Monitoring Independent Reader Performance


Though many clinical trials rely on medical image evaluations for primary or key secondary endpoints, the methods to monitor reader performance are all too often mired in the legacy use of adjudication rates. If misused, this simple metric can be misleading and sometimes entirely contradictory. Furthermore, attempts to overcome the limitations of adjudication rates using de novo or ad hoc methods often ignore well-established research conducted over the last half-century and can lead to inaccurate conclusions or variable interpretations. Underperforming readers can be missed, expert readers retrained, or worse, replaced. This paper aims to standardize reader performance evaluations using proven statistical methods. Additionally, these methods will describe how to discriminate between scenarios of concern and normal medical interpretation variability. Statistical methods are provided for inter-reader and intra-reader variability and bias, including the adjudicator's bias. Finally, we have compiled guidelines for calculating correct sample sizes, considerations for intra-reader memory recall, and applying alternative designs for independent readers.

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  1. search terms: Oncology, 2011–2020.

  2. search terms: Recruiting, Active, not recruiting, Completed, Suspended, Terminated, Withdrawn Studies | Interventional Studies | Oncology | imaging OR recist OR Lugano OR cheson OR MRI OR ct OR ultrasound OR pet OR rano OR Choi OR PFS OR ORR OR BOR | Phase Early Phase I, PhaseII, Phase III, Phase II/III.

  3. See ( See Fig. 1 and Online Resource 1 “A Description of Reader Symmetry).

  4. Note that the confidence limits provided in Ford 2016 need to be adjusted by the number of studies to establish an estimate of coverage.



Adjudication rate (the rate of disagreement between two readers evaluating the same patient)


Adjudicator selection rate (the rate that an adjudicator selects a reader from a paired team of two readers when those two readers disagree)


Blinded independent central review (the readers used by an Imaging Core Lab to assess the images scanned at an investigator site)


Confidence interval (to show the range of confidence in a parameter estimate)


Complete response (classification of response)


Date of progression (used for event-related endpoints like progression-free survival)


Fluid-attenuated inversion recovery (an MRI sequence used to suppress fluids)


Glioblastoma multiforme (a to date uncurable brain cancer)


Imaging Core Lab (a central facility that manages the BICR)


Intra-reader variability (the disagreement of readers with a previous assessment made on the same set of images)


Progressive disease (classification of response)


Partial response (classification of response)


Response evaluation criteria in solid tumors (an objective tumor size assessment criteria to categorize a patient’s response to treatment)


Stable disease (classification of response)


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The authors would like to express their sincere appreciation to Drs. Anthony Fotenos and Alex Hofling (FDA/CDER) and Dr. Joseph Pierro (eResearch Technology) for their valuable insight, participation, and contributions to the discussions and development of the methodologies within this manuscript. The authors would further like to acknowledge Liz Kuney's contribution for her valuable insight in developing and editing this manuscript and to the reviewers for their valuable and insightful comments.


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DLR and AMS both equally contributed to concept, design, drafting, finalizing and approved all content. CGM contributed to the concept, design, drafting, finalizing, and approval of all content. RCW contributed to the concept, drafting and finalizing all content. MO’C contributed to the concept, drafting, and finalizing all content. KN contributed to the concept, drafting, and finalizing all content. IH contributed to the concept, drafting, and finalizing all content. MO’N contributed to the concept, drafting, and finalizing all content. GB contributed to the concept, drafting, and finalizing all content. RRF contributed to the concept, design, drafting, finalizing, and approval of all content. All authors agree to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

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Correspondence to David L. Raunig Ph.D..

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Raunig, D.L., Schmid, A.M., Miller, C.G. et al. Radiologists and Clinical Trials: Part 2: Practical Statistical Methods for Understanding and Monitoring Independent Reader Performance. Ther Innov Regul Sci 55, 1122–1138 (2021).

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