Reliability of measuring trunk motions in centimeters.

A method of measuring trunk motion and two related motions using a tape measure and a stepstool was developed by physical therapists at our hospital. The purpose of this study was to assess the reliability of this method. Three repetitions of six motions performed by 24 subjects were each measured by three physical therapist raters on two separate days. The motions were forward bending, backward bending, right side bending, right rotation, right straight leg raising, and right prone knee bending. Reliability, standard deviation, and standard error were calculated for each motion. Only forward bending exhibited good single measurement reliability. Reliability coefficients for all motions were higher for the average of three successive measurements or for the measurement of a motion on successive days by the same rater. Measurements of rotation and straight leg raising, despite the improvement, continued to have low reliability. Analysis of variance was used to determine the significance of the differences between means for each motion across three raters, three repetitions, and two days. By looking at the analysis of variance and reliability estimates together, the authors identified two types of constant error affecting the data.