The positive and negative syndrome scale for schizophrenia

The modern debate about schizophrenia began over 100 years ago,
with Kraepelin’s description of “dementia praecox”. Despite this,
central aspects of the disease remain mysterious and the disease
itself is still associated with a high probability of an enduring
limitation of the patient’s quality of life. While several
conceptions of schizophrenia exist and are still under discussion,
at least a provisional consensus regarding a valid measure of
schizophrenia seems to have been reached: The Positive and Negative
Syndrome Scale (PANSS) quantifies the current state of a person
with schizophrenia by combining 30 different
schizophrenia-associated symptoms into a single scale value. Even
though the scale is widely used and is the measure of choice in
many clinical trials, its psychometric properties are still the
reason for serious confusion. In many research papers, one
important fact about the PANSS is overlooked: it is an interval
scale and, therefore, straightforward calculations of proportions
are not appropriate. In other words, calculating simple percentage
changes is incorrect and a prior scale correction is required.
These kinds of calculations often appear in conjunction with
responder analyses, as the definition of response is usually based
on a predefined cut-off in terms of percent scale change. Two of
the presented papers of this thesis are dealing with this urgent
problem: using real data as well as simulated data sets, it is
shown that ignoring the scale level of the PANSS can, in many
cases, even lead to false test decisions concerning an examined
treatment effect. Furthermore, an analysis of the problem’s urgency
with regard to academic discussions, performed by way of a
systematic study of literature in the highest-ranked journals
dealing with schizophrenia, showed that incorrect calculations are
widespread in the literature and that there is a strong need for a
general clarification. As incorrectly calculated percent changes
might be a reason for the published low cut-offs of response, as
e.g. 20% or 30% cut-offs, the third included article in this thesis
analyzes the association of correctly calculated percent changes in
the PANSS with a generally measured therapy response. An
equipercentile linking of percent PANSS changes and the improvement
item of the Clinical Global Impression Scale (CGI) confirmed the
choice of a considerably higher response cut-off of 50%. The
combined conclusion of the three included articles is the emphasis
on the need for a general methodological consensus in schizophrenia
research. Valid and replicable research is only possible on the
basis of generally accepted methods that rely on the correct
application of scale theory in these studies.