With six out of seven variables having an intraday correlation coefficient above 80 and the same six variables having an interday correlation above 70 we believed the IAPS method for determining postural changes was dependable. Depth of thoracolumbar curve was the one variable that demonstrated the lowest correlation coefficient for intraday and interday reliability. Because of the small range of D variability among healthy subjects, this low might be expected. The magnitude of the change in the absolute depth value was small but within the accuracy or the IAPS