Figure 3  .

Principal component analysis on change in joint space width measurements using four reading procedures in 104 patients with hip osteoarthritis. The first principal component accounts for 88.3% of the total variability. All the four coefficients are positive and nearly equal, thus allowing the assertion that this component is a measure of global time variation value. The second principal component opposes the single reading procedure without landmarks to the three other reading procedures. This component, which accounts for 9.8% of total variability, then reflects the advantage of using landmarks.