Objective Balance system and postural control are one of the major problems in people with multiple sclerosis. Therefore, the assessment of the balance system and postural control is very essential. Identification and use of standard tools can be a practical solution for more purposeful plan in this issue. Several tools have been used to investigate the balance disorders in these patients, which solely able to screen equilibrium problems, and only predict the risk of falling in the elderly. These questionnaires cannot help the therapist to diagnose the underlying causes of imbalance and also are not useful in directing the purposeful therapeutic process. The Balance Evaluation Systems Test (BESTest) was designed from 1990 to 1999 by Dr. Horak in the Continues Medical Education System. This questionnaire is based on the Bernstein’s theory of motor control, and the test evaluates Biomechanical, Stability Limits, Postural Responses, Anticipatory Postural Adjustments, Sensory Orientation, and Dynamic Balance through 36 questions. The objective of this study was to determine the validity and reliability of the BESTest evaluation system in patients with multiple sclerosis after providing a coherent version of the questionnaire in Persian.
Materials & Methods This is a methodological and non-experimental study. The BESTest questionnaire was translated by the researcher. The face validity of the questionnaire was evaluated by a survey of 21 patients with multiple sclerosis. The content validity of the questionnaire was further evaluated by a survey of 6 specialists in the field of rehabilitation (three occupational therapists and three specialists in the field of physiotherapy). After that, the BESTest questionnaire and Berg questionnaire were completed by two researchers (the author and another examiner) for 110 people diagnosed as multiple sclerosis, considering inclusion and exclusion criteria, from north, south, east, west, and center of Tehran in the years 2016-2017. After one week, 36 patients from the first stage were reevaluated in with a BESTest questionnaire by the researcher to evaluate the test-retest reliability. The internal consistency with Cronbach’s alpha coefficient, test-retest reliability by intra-class correlation coefficients traces, inter-rater reliability coefficients of correlation between the traces, and convergent validity between the two questionnaires (BESTest and Berg) with Pearson correlation coefficient were investigated.
Results The content validity of the questionnaire (the comprehensibility, relevance of the questions, and the cultural matching of words), which were measured by the CVR and CVI statistical methods, were approved by the specialist (CVI>0.79 and CVR>0.99). Pearson correlation coefficient between all the domains of the BESTest questionnaire (except for the second domain) with the score of the Berg questionnaire was between 0.79 and 0.93. Given that the numbers are above the minimum acceptable value of 0.70 indicates a good convergence between these two questionnaires. By removing a part of a 6th item from the second domain, the Cronbach’s alpha coefficient calculated in all domains were between 0.71 and 0.93, which were much higher than the minimum acceptable value of 0.70. These results indicate an excellent internal consistency. Correlation coefficients between two testers in six domains were reported 0.76 to 0.98. Therefore, these coefficients were above 0.70 in all domains, which indicates the good reliability between two examiners. Furthermore, the Intra-sectional correlation coefficient for two repetitions of the questionnaire for the test-retest reliability of the test were 0.84 to 0.99, which were higher than 0.70 (minimum acceptable), which shows that the questionnaire has an excellent test-retest reliability. 
Conclusion  After changing and removing part of question 6 of the second domain, results demonstrated that the questionnaire BESTest is a valid and reliable test for assessing balance performance in multiple sclerosis patients. It can be used as an accurate tool, both in the areas of clinical (to evaluate the patients’ equilibrium status and purposeful therapy planning) and to apply for scientific research in patients with multiple sclerosis.