There is currently one trial in which a relatively large number of
patients with negative erosion scores supports repair occurring on a group level [4]. Although the appraisal of repair on a
group level is a relatively simple statistical matter, translating
repair from the group level to an individual patient is not
straightforward. The null hypothesis that there is no change
from baseline within the group can be rejected if the mean
change is below zero and the entire 95% confidence limit is
below zero, which occurred in the TEMPO trial [11]. In contrast, a negative change score in an individual patient can be
composed of 'true repair', of measurement error or of an image
artefact such as rotation hiding a tangential erosion. The interrelationship of these three components is unknown and different in each patient. This argument is also pertinent in
evaluation progression scores.