Open Access Research article

Procedures for assessing psychological predictors of injuries in circus artists: a pilot prospective study

Ian Shrier1*, John S Raglin2, Emily B Levitan3, Murray A Mittleman4, Russell J Steele5 and Janette Powell6

Author Affiliations

1 Centre for Clinical Epidemiology, Lady Davis Institute for Medical Research, Jewish General Hospital, 3755 Ch. Côte Ste-Catherine, Montréal H3T 1E2, Canada

2 Kinesiology Department, Indiana University, Indianapolis, Indiana, USA

3 Department of Epidemiology, University of Alabama at Birmingham School of Public Health, Birmingham, Alabama, USA

4 Cardiovascular Epidemiology Research Unit, Department of Medicine, Harvard Medical School, Harvard University, Boston, Massachusetts, USA

5 Department of Mathematics and Statistics, McGill University, Montreal, Canada

6 Performance Medicine “O”, Cirque du Soleil, Las Vegas, USA

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BMC Medical Research Methodology 2014, 14:77  doi:10.1186/1471-2288-14-77

Published: 11 June 2014



Research on psychological risk factors for injury has focused on stable traits. Our objective was to test the feasibility of a prospective longitudinal study designed to examine labile psychological states as risk factors of injury.


We measured psychological traits at baseline (mood, ways of coping and anxiety), and psychological states every day (1-item questions on anxiety, sleep, fatigue, soreness, self-confidence) before performances in Cirque du Soleil artists of the show “O”. Additional questions were added once per week to better assess anxiety (20-item) and mood. Questionnaires were provided in English, French, Russian and Japanese. Injury and exposure data were extracted from electronic records that are kept as part of routine business practices.


The 43.9% (36/82) recruitment rate was more than expected. Most artists completed the baseline questionnaires in 15 min, a weekly questionnaire in <2 min and a daily questionnaire in <1 min. We improved the formatting of some questions during the study, and adapted the wording of other questions to improve clarity. There were no dropouts during the entire study, suggesting the questionnaires were appropriate in content and length. Results for sample size calculations depend on the number of artists followed and the minimal important difference in injury rates, but in general, preclude a purely prospective study with daily data collection because of the long follow-up required. However, a prospective nested case-crossover design with data collection bi-weekly and at the time of injury appears feasible.


A prospective study collecting psychological state data from subjects who train and work regularly together is feasible, but sample size calculations suggest that the optimal study design would use prospective nested case-crossover methodology.

Epidemiology; Injury; Psychological risk factors; Prospective