Estimating the accuracy of muscle response testing: two randomised-order blinded studies

Test methods

TPs spoke 40 statements of mixed verity as follows. They viewed pictures on a computer screen placed out of view of the practitioners. While viewing a picture selected at random by computer, the TPs were given instructions by computerised voice via an earpiece inaudible to the practitioners. Instructions took the form, “Say, ‘I see a ________.’” The verity of the statements (that is, whether the instructed statement was chosen to match the picture on screen) were randomly allocated by software (DirectRT Research Software, Empirisoft Corporation, New York, NY), with overall prevalence of lies set to be 50?±?3%. The practitioner also viewed a computer screen and was randomly shown either the same picture as the TP (i.e. not blind) or a blank black screen (i.e. blind). Participants were blind to study aims and were not informed of the proportions of True/False statements or Blind/Not Blind cases. Pictures of neutral valence (i.e. emotionally neutral) were chosen from the International Affective Picture System (IAPS; National Institute of Mental Health Center for Emotion and Attention, University of Florida, Gainesville, FL) [21] and paired with neutral words selected from the Affective Norms for English Words (ANEW; National Institute of Mental Health Center for Emotion and Attention, University of Florida, Gainesville, FL) [22].

Following each statement spoken by the TP, the practitioner was asked to estimate the verity of the statement: ten times using MRT, followed by ten times using intuition alone, and alternating in blocks of ten thereafter (see Additional file 5: Figure S1). The practitioner entered their estimate for each statement by single key press on a keyboard connected to the study computer, which automatically collated results. Practitioners and TPs were allowed a short period to familiarise themselves with study layout and procedures before beginning, and the principal investigator was present in the room during data collection but did not take part.

Participants were asked to complete two short questionnaires, one before testing started and one after testing was completed. The TP Pre-testing Questionnaire included questions about age, gender, handedness, MRT experience, and levels of confidence in MRT, in their practitioner, and their practitioner’s MRT. The practitioner pre-testing questionnaire included questions about age, gender, handedness, type of practitioner, years in practice, years of MRT experience, self-rated MRT expertise, specific MRT techniques used, and levels of confidence in MRT in general and their own MRT ability. Levels of confidence were measured using a 10 cm Visual Analogue Scale (VAS) with the left end marked “None” and the right end marked with “Complete Confidence.” All participants were asked to use a “|” to mark the VAS, which was subsequently assigned a score out of 10. Practitioners were asked to rate their own MRT expertise using a 5-point Likert scale from 0 (None) to 4 (Expert). We combined categories 1 and 2 of self-reported expertise due to low numbers (e.g. n?=?1 whose reported their expertise was at level 1). Lengths of time, such as ages and years in practice, were kept as continuous variables, while other variables, such as gender, profession, and MRT techniques used, were kept as categorical variables.

In the Post-testing Questionnaire, participants were again asked to rate the same levels of confidence. In addition, in the Post-testing Questionnaire, TPs were asked to make open-ended comments about anything they noticed during the MRT, in order to establish if they deduced the paradigm under investigation (i.e. lies result in a “weak” MRT response), so that response bias can be measured [23, 24]. As a means of fidelity assurance during this experiment, the principle investigator (AJ) was present during all testing and assessment.