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st: RE: new program sampsi_sccs


From   "Lachenbruch, Peter" <Peter.Lachenbruch@oregonstate.edu>
To   <statalist@hsphsun2.harvard.edu>
Subject   st: RE: new program sampsi_sccs
Date   Mon, 20 Apr 2009 09:04:46 -0700

I downloaded this program and played with it a bit.  Here is one bit of
output.  At the end you may note that the number of events required in
unexposed subjects if -6.  I may have chosen dopey inputs, but I don't
think I can envision any group with -6 events.  Phil - or someone - can
you help?  I tried another combination and got -6 events needed...

. sampsi_sccs, rho(3) method(age)

Signed root likelihood method controlling for age effects

input number of age groups    (e.g. 5)
. 5


input age specific incidence [relative to age group 1] in age group 2
. 3
input age specific incidence [relative to age group 1] in age group 3
. 5
input age specific incidence [relative to age group 1] in age group 4
. 7
input age specific incidence [relative to age group 1] in age group 5
. 7


input length of observation period for age group 1
. 10
input length of observation period for age group 2
. 10
input length of observation period for age group 3
. 10
input length of observation period for age group 4
. 10
input length of observation period for age group 5
. 10


input post exposure risk period [assumed the same for each group]
. 10


input proportion of subjects exposed during obs period in age group 1
. .2
input proportion of subjects exposed during obs period in age group 2
. .2
input proportion of subjects exposed during obs period in age group 3
. .3
input proportion of subjects exposed during obs period in age group 4
. .3
input proportion of subjects exposed during obs period in age group 5
. .3

==================================================================
========== sample size for SCCS Design with age effects ==========
==================================================================

  2-tailed alpha is:                                       .05
  power is:                                                .8
  relative incidence associated with exposure is:          3
  common post-exposure risk period is:                     10


  total number of events required in exposed subjects is:   32

  total number of events required in unexposed subjects is: -6

  Total number of events required is:                       26
==================================================================

.

Tony

Peter A. Lachenbruch
Department of Public Health
Oregon State University
Corvallis, OR 97330
Phone: 541-737-3832
FAX: 541-737-4001


-----Original Message-----
From: owner-statalist@hsphsun2.harvard.edu
[mailto:owner-statalist@hsphsun2.harvard.edu] On Behalf Of Philip Ryan
Sent: Sunday, April 19, 2009 4:31 PM
To: statalist@hsphsun2.harvard.edu
Subject: st: new program sampsi_sccs

Listers

Thanks again to Kit Baum, a new program -sampsi_sccs- is now available
on
the SSC server.

-sampsi_sccs- calculates sample sizes for self-controlled case series
study
designs. Full refs to a tutorial on this type of study and to Musonda et
al's paper on sample size estimation are included in the accompanying
help
file.


Requires Stata v10

To check it out:

ssc describe sampsi_sccs


Philip Ryan
University of Adelaide
South Australia


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