The longitudinal sensitivity of a technique, i.e., its ability to monitor s
keletal changes, is affected by two parameters: the long-term precision err
or (PEIt) and the subject group-specific response rate (i.e., annual rates
of change), Both need to be considered to avoid misinterpretation of measur
ed changes. A new concept to aid clinical decision making for longitudinal
measurements is proposed which is based on three types of measures: criteri
a for detecting changes-the "least significant change" (LSC) is the smalles
t change to be considered statistically significant, but for certain clinic
al questions a smaller margin, the "trend assessment margin" (TAM), can be
sufficient for decision making; follow-up time intervals-for follow-up exam
s the patient should be called in at about the time interval specified by t
he (population specific) "monitoring time interval" (MTI) or, about one-thi
rd of the time earlier, after the "trend assessment interval" (TAI), depend
ing on whether the decision can be based on the LSC or the TAM; and the sta
ndard precision error (stdPE)-the smaller stdPE, the more sensitive the tec
hnique to monitor skeletal changes. Together, these three measures yield a
good characterization of a technique's ability to monitor skeletal changes.
Compared with previous concepts, the proposed standardization by a respons
e ratio instead of measures of spread or response rates makes the stdPE sub
stantially less subject group dependent. It allows comparison of stdPE acro
ss different studies and could replace the misleading concept of expressing
precision as a coefficient of variation. Application of this concept shoul
d facilitate the interpretation of measured skeletal changes.