Hi Cathy
For a pilot RCT the attached paper recommends 30 per group, and then you add on to that according to expected level of drop out.
Lancaster GA, Dodd S & Williamson PR. (2004). Design and analysis of pilot studies: recommendations for good practice. Journal of Evaluation in Clinical Practice 10(2), 307-312.
Best wishes
Alison
Alison Cooke
Research Midwife
School of Nursing, Midwifery and Social Work
The University of Manchester
and
Central Manchester NHS Foundation Trust
Maternal and Fetal Health Research Centre
5th Floor, Research
St Mary's Hospital
Oxford Road
Manchester
M13 9WL
Tel 0161 276 5469
________________________________________
From: A forum for discussion on midwifery and reproductive health research. [[log in to unmask]] on behalf of Cathy Walton [[log in to unmask]]
Sent: 01 June 2012 15:24
To: [log in to unmask]
Subject: Re: Advice wanted
Yes- that's right and in fact we are looking back over our CS rates.
Does seem abit chicken and egg in terms of what you need to know to do a
power calculation as the sample needs to be big enough to detect a
difference but also to do a calculation you need to know what difference
you might be looking for....
What about for a pilot study of the same study with the same primary
outcome?
Thank you for your thoughts.
Best wishes,
Cathy
On 01/06/2012 15:01, Carolyn Roth wrote:
> Right, having re-read the question, I see your point. So in effect, you
> are looking to set the (arbitrary) level against which to judge
> statistical significance?
>
> Might one way of doing it be on the basis of changes to rates over time.
> i.e. use the LSCS rate of 1,3 or 5 years ago?
>
>
> Carolyn Roth
> Director of Undergraduate Programmes and LME
> School of Nursing& Midwifery
> Keele University
> Clinical Education Centre
> Newcastle Road
> Stoke-on-Trent
> ST4 6QG
>
> Tel. 01782 679698
>
>> Hi Carolyn,
>> We have and in order to do a power calculation she asked me to try to find
>> this out.
>> Best wishes,
>> Cathy
>>
>> On 1 Jun 2012, at 12:47, "Carolyn Roth"<[log in to unmask]> wrote:
>>
>>> Hi Cathy, Can't answer your question, but I would have thought you need
>>> to
>>> talk to a statistician with the details of the proposal to get the
>>> advice
>>> you need.\\
>>>
>>>
>>> Carolyn Roth
>>> Director of Undergraduate Programmes and LME
>>> School of Nursing& Midwifery
>>> Keele University
>>> Clinical Education Centre
>>> Newcastle Road
>>> Stoke-on-Trent
>>> ST4 6QG
>>>
>>> Tel. 01782 679698
>>>
>>>> Dear Midwifery research group members,
>>>> I am a consultant midwife at King's College Hospital in London and have
>>>> been a member of this group for a number of years and rarely contribute
>>>> but always find the discussions interesting. Sadly, I don't get to do
>>>> much research in my job, as it really isn't easy to have time for it.
>>>> However, recently I have been involved in the planning of 2 possible
>>>> RCTs and would like to pick the brains of the esteemed members of this
>>>> list.
>>>>
>>>> Would anyone have any suggestions for what would be a clinically
>>>> significant % point reduction in the casaerean section rate if used as
>>>> a
>>>> a primary outcome?
>>>> If so, can you direct me to any evidence or reference that might be
>>>> useful to base this on?
>>>>
>>>> Many thanks,
>>>> Cathy Walton
>>>>
>>>
>
> Carolyn Roth
> Director of Undergraduate Programmes and LME
> School of Nursing& Midwifery
> Keele University
> Clinical Education Centre
> Newcastle Road
> Stoke-on-Trent
> ST4 6QG
>
> Tel. 01782 679698
>
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