Announcements/News
Highlights
- Dr. Hays' response to
"What is Important to Patients? Quantity or Quality of Life? By
Allen Nissenson, MD, posted in Quality"
(https://plus.google.com/+RonHaysUCLA/posts/T5txeY3Uek4)
Nissenson's blog says the following: “As shown recently by Tracy
Mayne, an international authority in this area and a member of
DaVita Clinical Research® (DCR®). KDQOL cannot be validated as truly
predictive of QOL with current ESRD patients.”
My response (comment) to this statement was submitted to Nissenson's
blog on June 26, 2016 @ 2:10 pm (does not appear that it was
accepted as a post yet by Nissenson). The response is reproduced
below.
Not sure what you are referring to by this vague comment, but this
presentation of results from 32,926 KDQOL-36 surveys reveals a
superficial understanding of psychometric methods:
http://www.davitaclinicalresearch.com/wp-content/pdfs/ASN_2010/SA-PO2616-ASN2010_KDQOL_Valid_8Nov10DVW.pdf
The poster summarizes results of a factor analysis, item-scale
correlations, and internal consistency reliability. The summary of
results states that the data “do not confirm 2-factor solution” for
the SF-12 in dialysis patients.
The methodology is described as a confirmatory factor analysis, but
apparently this was really an exploratory principal components
analysis. Despite the claim that a 2-factor solution was not
confirmed, the scree plot for the SF-12 in Figure 1 can be
interpreted as 2 principal component eigenvalues prior to the
“scree.” The third principal component eigenvalue is 1.03–barely
larger than eigenvalue > 1.0 criteria for possible number of factors
(i.e., Guttman’s weakest lower bound rule of thumb).
Similarly, the second principal component eigenvalue for the burden
scale is 1.09, again not much larger than Guttman’s weakest lower
bound and the scree plot supports a single underlying dimension.
In addition, it is stated that a Varimax (uncorrelated) factor
rotation was conducted despite the fact that the SF-12 physical and
mental health scores are know to be associated significantly and
substantially (correlations of 0.40-0.60).
The statement that MCS explains only 12% of the scale variance is
inaccurate. The second principal component eigenvalue accounts for
that proportion of variance but the second component is not the same
as the MCS.
Cronbach’s alphas are reported for the SF-12 physical and mental
health summary scores, but coefficient alpha is not appropriate for
a weighted combination of items. The fact that negative item-total
correlations are reported suggests a potential problem with how the
data were scored.
There is a good distribution of scores and ceiling effects do not
appear to be excessive, despite the note about “significant” floor
and/or ceiling effects.
Alpha is mispelled as “alfa” a few times. The term, “Internal
Validity,” in the title does not make sense.
This study does not provide information on validity (whether the
KDQOL-36 measures what it is supposed to assess).
Ron Hays
- KDQOL-SF™
The KDQOL-SF scoring program is available for download - please
visit our downloads page for
information.
- KDQOL-36
The KDQOL-36 is short form that includes the SF-12 as generic
core plus the symptoms/problem, effects of kidney disease, and
burden of kidney disease scales from the KDQOL-SF. The
PDF version is now available on our
downloads page.
(To access download page, register
first to get username/password).
