Purpose: We investigated the minimum number of measurements needed for reproducibility of the simple reaction time, the vocal response to an auditory signal, in sitting, standing and supine. Subjects: The subjects were 34~36 physical therapy students, and 24~27 healthy elderly persons who participated in government sponsored physical strength measurement and exercise guidance for falls prevention, who had no history of orthopedic or central nervous system disorders. Method: The simple reaction time was measured 10 times in sitting, standing and supine. We investigated the reproducibility as well as the number of consecutive measurement times needed for there to be no difference from the average of 10 measurements using the intra-class correlation coefficient (ICC (1,1)) and the paired t test. Results: For young people, the minimum number of repeated measurements delivering a value which was not significantly different from the average of 10 measurements and having an ICC(1,1) ≥0.9 was 2~3 in sitting, 1~2 in standing, and 3~4 in supine. Similarly for the elderly subjects, the number of times was 3~4 in sitting, 3~4 in standing, and 2~3 in supine. Conclusion: The results suggest that measurements need to be made 3 times with young subjects and 4 times with old subjects if the measurement times are unified for the 3 positions.
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