Mnd. Lassere et al., Robustness and generalizability of smallest detectable difference in radiological progression, J RHEUMATOL, 28(4), 2001, pp. 911-913
The smallest detectable difference (SDD) reflects that component of a measu
re statistically attributable to error from the measurement process itself.
As such it is an irreducible component of the inherent variability in meas
urements in clinical trials and will affect their design, whether randomize
d or observational. Even though the application of the SDD concept to assay
ing radiographs in rheumatoid arthritis is relatively new and not well unde
rstood, systematic work on the influences of radiographic SDD can be done.
This report describes the effects of a number of clinical aspects of the di
sease and operational aspects of trials on the values of the SDD of radiogr
aphic progression data. We show that if conditions affecting SDD are known
and kept constant across datasets, the SDD of radiological progression from
one study may be generalizable to other studies. However, if any one condi
tion varies, the SDD is distinctly unrobust and cannot be generalized to ot
her studies.