Extract
Riddle and Lingard make an important point that supports our sentiments
that the implications of response shift in orthopaedic clinical research are
potentially profound and needs to be considered. These authors, however, raise
concern about the Then-Test methodology in measuring response shift.A growing body of literature has examined the impact of response shift in
patients. Schwartz et
al.5, in a recent
metaanalysis of response shift-related articles, reported that the majority of
reviewed articles (from 1966 to 2004) involved the Then-Test design.
Furthermore, it was only those studies that were able to provide requisite
data for effect size computation. Other responseshift studies involving the
use of individualized measures, such as the Patient-Generated Index, Schedule
for the Evaluation of Individual Quality of Life (SEIQoL), or qualitative
interviews, did not provide the data necessary for calculating effect
size.
Riddle and Lingard make an important point that supports our sentiments
that the implications of response shift in orthopaedic clinical research are
potentially profound and needs to be considered. These authors, however, raise
concern about the Then-Test methodology in measuring response shift.
A growing body of literature has examined the impact of response shift in
patients. Schwartz et
al.5, in a recent
metaanalysis of response shift-related articles, reported that the majority of
reviewed articles (from 1966 to 2004) involved the Then-Test design.
Furthermore, it was only those studies that were able to provide requisite
data for effect size computation. Other responseshift studies involving the
use of individualized measures, such as the Patient-Generated Index, Schedule
for the Evaluation of Individual Quality of Life (SEIQoL), or qualitative
interviews, did not provide the data necessary for calculating effect
size.
The Then-Test method assumes that respondents will use their Post-Test
internal standards when providing a reevaluation rating of their baseline
score. We acknowledge that the Then-Test design has been criticized for its
susceptibility to recall bias. This was evaluated by Visser et
al.2 in a convergent
validity study. Those authors measured response shift with the Then-Test
approach, anchor recalibration, and structural equation modeling. They showed
good convergent validity between the Then-Test approach and structural
equation modeling. The results of both of these methods were largely
comparable. This finding suggests that the structural equation modeling and
the ThenTest approach measure the same concept. These methods use
statistically independent operations for response shift. Structural equation
modeling does not use retrospective data and is, therefore, not susceptible to
recall bias. Based on the convergence of methods for their results, this
suggests that the ThenTest was not affected by recall bias.
Generalizability to other Then-Test studies is not necessarily guaranteed.
Visser et al.6 used
a testing interval of three months; in our study, an interval of six months
was used. Further studies comparing the Then-Test and structural equation
modeling of large intervals are needed to determine whether the convergence of
methods will still show good convergent validity at six months. As such, we
agree with Riddle and Lingard that additional study is required to further
define the role of response shift and the potential limitations in our ability
to accurately measure this phenomenon.
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