dear all
a problem is puzzling us
we have a RCT design; to simplify a bit: the primary outcome of interest
is in effect a test (patient recall of being asked about their smoking
by their GP); data suggests a sensitivity of approx 90% and specificity
80%. The PPV (which is the necesaary link between the test and the
outcome of interest) will therefore vary depending upon the prevalence
of the target condition (whether a patient was asked about their smoking
at the last consultation with a GP). The trial intervention is designed
to affect this target condition (to increase the prevalence); therefore
the PPV of the test will vary in a way that we cannot predict. (and
whose only measure is the PPV; which becomes a circular argument))
This seems to introduce another source of error affecting our ability to
be confident about the effect of the intervention.
Is this a significant problem or am I missing something?
Have others had to deal with this; if so how?
presumably this is a common trial problem when the outcome is measured
via a test (less than 100% accurate)of any sort; has anything been
written about this?
TIA; you're my last hope
O
Owen Dempsey
General Practitioner
Senior Research Fellow
Centre for Research in Primary Care
Hallas Wing
Nuffield Institute for Health
71-75 Clarendon Road
University of Leeds
Leeds LS2 9PL
work: 01484-460298 (practice)
work 0113-233-4835 (Leeds office)
home: 01484-654794
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