Nilesh,
The risk of excluding people following randomisation is that it may
introduce systematic bias. eg if the inclusion/exclusion criteria were
checked more rigourously for those people who had a worse outcome.
The ideal situation would be to ensure that only people who met the
inclusion/exclusion criteria were randomised. In real life it oftens
happens that non eligible patients are randomised. So long as this
proportion is small, it is unlikely to have a major effect on the
outcome of interest. If the proportion is large (say >10%), then this
questions the overall validity of the trial. You can always perform an
intention to treat analysis of all patients and compare this with an
analysis of eligible patients (or an analysis of treatment received), to
get some idea of how similar they are. however, if there are large
differences between the two approaches, this can create difficulties re
interpretation of the results.
Hope this is of some help
Peter Ellis
Dr Nilesh Patel wrote:
>
> Dear All
>
> Is the following reasoning correct?
>
> When evaluting the validity of trial about a therapy, ensuring that all
> patients are analysed in an intention to treat manner is important since
> the percentage of compliers versus non-compliers may be different in the
> placebo and intervention groups. In this way we are testing whether the
> offering of a specific treatment is more beneficial than offering placebo.
>
> Now when analysing whether patients would benefit from a series of services
> organised in a certain manner (e.g. stroke unit treatment) compared to
> routine care, how do you analyse patients who only at the end of (or
> during) the trial are found not to meet the inclusion criteria (e.g. not a
> stroke but a cerebral metastasis)?
>
> Surely because the entry criteria are not met, the patients should be
> excluded BEFORE the analysis. This is not the same as someone being
> allocated to the stroke unit and decides not to be admitted for any reason
> (e.g. the unit may be at another hospital). The latter would be analysed
> including the patient as "a patient who the trial intended to treat".
>
> Is my reasoning correct?
>
> Dr Nilesh Patel
> Director: Clinical Services
> The Brenthurst Centre for Rehabilitation Medicine
> Johannesburg
> South Africa
--
Peter Ellis MBBS FRACP MMed(Clin Epi)
Research Fellow
Dept Medical Psychology Royal Prince Alfred Hospital
Dept Cancer Medicine Sydney University
Ph: 61 2 9515 7618
Fax: 61 2 9515 5697
email: [log in to unmask]
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