Have you looked at the outcome measures of similar RCTs for example Vanora
Hundley's study in Aberdeen or the Glasgow Royal Maternity RCT
Turnbull et al (1996) Randomised controlled trial of efficacy of
midwife-managed care. Lancet 348: 213-218
Hundley et al (1994) Midwife managed delivery unit: a randomised controlled
comparison with consultant care. British Medical Journal. 309: 1400-1404.
There are of course others and they should give you somewhere to start
Helen Cheyne
-----Original Message-----
From: ddevane [mailto:[log in to unmask]]
Sent: Friday, October 18, 2002 1:24 PM
To: [log in to unmask]
Subject: sample size
Dear all,
I am trying to estimate sample size for an RCT comparing midwifery-led units
to consultant-led care and have come across an ambiguous difficulty and it's
not related to estimating sample size with power analyses!
I am aware that the primary question is what the sample size is based on.
The main outcome of investigation of the trial is safety but this causes
difficulties. Maternal mortality is non runner as it is so rare in excess
of 269,000 women would be needed to link causality and the same argument,
although a smaller sample would be needed, is used in regard to neonatal
mortality. So we are left with morbidity outcome measures as a measure of
safety and a decision as to which to choose as the primary question.
Admission of babies to neonatal intensive care units is impractical because
to show a difference between 8% and 6% admitted would require in excess on
6000 women to be randomised. Safety is certainly important but a broad
concept but which outcome should be chosen. Most importantly, I want to
choose an outcome that is realistically achievable within the RCT. Perhaps
I should look at other outcome measures that are important and more common
and would any of these be regarded as addressing 'safety'?
Thanks for advice
Declan
Declan Devane,
Doctoral Student,
School of Nursing and Midwifery Studies,
University of Dublin Trinity College,
Trinity Centre for Health Sciences Education,
St. James's Hospital,
Dublin 8.
Tel: 087 659 6923
Email: [log in to unmask]
*******************************************
Please note that electronic mail to,
from or within Trinity College may be
the subject of a request under the
Freedom of Information Act
*******************************************
--
The University of Stirling is a university established in Scotland by
charter at Stirling, FK9 4LA. Privileged/Confidential Information may
be contained in this message. If you are not the addressee indicated
in this message (or responsible for delivery of the message to such
person), you may not disclose, copy or deliver this message to anyone
and any action taken or omitted to be taken in reliance on it, is
prohibited and may be unlawful. In such case, you should destroy this
message and kindly notify the sender by reply email. Please advise
immediately if you or your employer do not consent to Internet email
for messages of this kind. Opinions, conclusions and other
information in this message that do not relate to the official
business of the University of Stirling shall be understood as neither
given nor endorsed by it.
|