Variability and reliability of joint measurements.

The purpose of this study was to determine the variability and reliability of joint measurements as carried out by three physician observers. The intratester variation and reliability of nine different joint measurements was determined in eight healthy subjects. The measurements were taken in eight sessions by each tester. In this population also the intertester variation and reliability was determined by the three observers. This was also done in a population of middle-aged athletes over a period of 2.5 years. The results indicate that it is difficult to show either an improvement or worsening of a joint motion of less than 5 degrees to 10 degrees for most joints measured by the same tester. The intertester variation is not consistent over a longer period of time, so differences between observers during long-term studies cannot be corrected on the basis of a single study at a single point in time. The reliability of all nine joint measurements is not very high, but is probably sufficient if the results are used to compare groups within a single population and for large studies with experienced observers. Because the reliability strongly depends on the interindividual variation, it is preferable to determine the reliability for each study population.