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st: R: applying sampsi: sub-groups

From   "Carlo Lazzaro" <>
To   <>
Subject   st: R: applying sampsi: sub-groups
Date   Thu, 7 Feb 2008 10:37:16 +0100

Dear Michael,
as far as I am concerned, what you outlined in your post already happened.

In this clinical trial (please, see full reference below), patients were
randomized to moxifloxacin (1st arm) or to one out of three antibiotics (2nd
arm), chosen according to physicians'opinion. Clinical as well as
microbiological results reported by patients enrolled in the 2nd arm of the
trial were pooled and compared with those repored by patients enrolled to
receive moxifloxacin (1st arm). 

Wilson R, Allegra L, Huchon G, Izquierdo JL, Jones P, Schaberg T, et al;
MOSAIC Study Group. Short-term and long-term outcomes of moxifloxacin
compared to standard antibiotic treatment in acute exacerbations of chronic
bronchitis. Chest 2004; 125: 953-964.

On the grounds of my experience in the economic evaluation of healthcare
programmes, I would take the liberty to advise you to carefully consider
whether this study design may cast some doubts on the robustness (even from
a statistical point of view)of the results as far as readers (or the
referees) are interested in head-to-head comparisons (ie, new treatment vs
1st standard treatment dose of the drug administered in the control group;
new treatment vs 2nd standard treatment of the drug administered in the
control group; new treatment vs 3rd standard treatment of the drug
administered in the control group).

HTH and Kind Regards,

-----Messaggio originale-----
[] Per conto di Michael McCulloch
Inviato: mercoledý 6 febbraio 2008 23.09
A: Statalist
Oggetto: st: applying sampsi: sub-groups

I am applying sampsi to a project design, and am puzzled by a 
question which perhaps one of the list members may have an opinion.

In my study design, subjects are randomized to one of two groups, 
treatment and control. Treatment group receives the new intervention, 
and control groups receives standard care.

My question is the following: after random allocation, within the 
treatment group subjects will be assigned to one of three treatment 
doses of the same treatment, depending on a differential diagnosis. 
In practice, in estimating sample size requirements, would one 
consider the three sub-groups as distinct groups, or aggregate them 
all into the treatment group?

Thank you.


Best wishes,
Michael McCulloch

Pine Street Foundation
124 Pine St., San Anselmo, CA 94960-2674
Tel:	(415) 407-1357
Fax:	(415) 485-1065
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