To The Editor:
In the paper "Response Shift in Outcome Assessment in Patients
Undergoing Total Knee Arthroplasty," (2006;88:2590-5), Razmjou and
colleagues concluded that patients demonstrated a response shift and that this
finding supports the need for accounting for response shift in clinical
research. The implications of these findings are potentially profound. Unless
authors account for response shift in randomized trials, for example, the
findings should be questioned.
The authors may indeed be right because response shift appears to be
real1,2. However, we have a concern about the way in which the
authors quantified response shift. The authors used the Then-Test approach to
measure response shift. In this case, each patient completed a WOMAC
questionnaire preoperatively and then completed two additional WOMAC
questionnaires at six months postoperatively. At six months, one questionnaire
(the Post-Test) was used to measure the current status and the second
questionnaire (the Then-Test) was used to measure the patient's recall of the
preoperative status. In other words, the Then-Test assumes that because more
information is available to the patient following surgery, it is more valid
than serial change scores for detecting real change. When using the Then-Test,
one must assume that patients accurately recall what their actual status had
been several months previously and then adjust their WOMAC ratings based on
the newly adjusted internal standard. However, this assumption has been
challenged by others3. In addition, the implicit theory of change
suggests that patients begin with their present state and infer what their
initial state must have been. An inherent part of this theory is that recall
of a previous state will be directly influenced by the patient's current state
and that the recall data will be biased and inaccurate4.
We agree that Razmjou and colleagues examined a potentially important issue
but question the use of the Then-Test to adjust for response shift for
clinical studies of arthroplasty. It confers considerable burden on the
patients, and the accuracy of recall is questionable, especially as the length
of time following surgery increases. Given the uncertainty in this area,
additional study is essential to correctly direct changes in the way that
clinical studies and trials are designed and conducted.