Same Question, Different Scores: Exploration of Two Possible Influences on the Variability between Spot Scores for the BOST

Donald J.  Krapohl; Donald Grubin; Ian Dersley

doi:10.31749/2380-0550-EP2026-1-02

Published: 30-06-2026

Vol. 20 No. 1 (2026)

Same Question, Different Scores: Exploration of Two Possible Influences on the Variability between Spot Scores for the BOST

Donald J. Krapohl , Donald Grubin , Ian Dersley

Section: Articles

https://doi.org/10.31749/2380-0550-EP2026-1-02

Abstract

The British One-issue Screening Test is a single-issue polygraph method intended for screening
examinations. Although its two relevant questions are virtually the same we have found there
to be a large average difference between the total scores for each. We undertook a 21-month
study to identify possible contributors to this finding. In one condition examiners used two
identical relevant questions. In the other condition examiners used slightly different verbiage
for the two relevant questions, but the pretest instructions were modified. Using a large sample
of control cases, we found no differences between the control samples compared with the use
of two identical relevant questions, but there was a significant effect when there was a change
in pretest instructions. Implications of this finding are discussed, including possible effects of
priming and habituation.

Keywords:

British One-issue Screening Test , Empirical Scoring System , score variability

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Krapohl, D. J., Grubin, D., & Dersley, I. (2026). Same Question, Different Scores: Exploration of Two Possible Influences on the Variability between Spot Scores for the BOST. European Polygraph, 20(1), 25–35. https://doi.org/10.31749/2380-0550-EP2026-1-02

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Donald J. Krapohl

Affiliation:

American Polygraph Association, United States

Bio Statement (e.g., department and rank)

Past President of the American Polygraph Association and a regular contributor
to this journal. Comments and suggestions should be sent to him at APAkrapohl@gmail.com

Donald Grubin

Affiliation:

Newcastle University, England., United Kingdom

Bio Statement (e.g., department and rank)

Don Grubin is Emeritus Professor of Forensic Psychiatry at Newcastle University, England.

Ian Dersley

Bio Statement (e.g., department and rank)

Ian Dersley is a PCSOT polygraph examiner in the Yorkshire and Humber and North East Regions
of the UK National Probation Service. The authors express their gratitude to the examiners
who provided the data used in this study: James Cook, Michael Reddish, Tracey Little, James Fraser,
Harriet Gregan, Brad Hughes, Ian Dersley, Jo Scully, Bernard Morris and Caroline Perrell. This
project would not have been possible without their assistance. The views expressed are solely those
of the authors and do not necessarily represent those of their respective employers or affiliations.
Conflict of Interest: The authors declare they have no conflicts of interest in this study.

Vol. 20 No. 1 (2026)
Published: 30-06-2026

ISSN: 1898-5238

eISSN: 2380-0550

Publisher

AFM Publishing House of the Andrzej Frycz Modrzewski Krakow University

Licence CC

This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.

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