Timing of outcome assessment

This section contains the following:


Once it has been decided what to measure (see Outcome measures ), it is important to consider when outcomes should be measured.  Typically, the period of follow-up should be sufficient to ensure that the wider range of effects, other than those that are evident immediately after the intervention is introduced, are observable.  If quality of life measures are to be included, it is also important to consider whether a baseline assessment should be included (required if the researcher wishes to evaluate any changes in a participant’s well-being during or after treatment).  The timing of each outcome measurement should be made explicit.

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Things to consider when writing a protocol

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Illustrative example - Perinatal care trial

Table 4 presents the components and the schedule for data collection in the project. There are three different sets of data to be collected, and the data collection system will be different for each one. These are

  • clinical outcomes,

  • readiness to change questionnaire to health providers, and

  • process measures.

Clinical outcomes and readiness to change questionnaire includes the primary and secondary outcomes of the project and will be measured in all participating hospitals (intervention and control arm). Process measures will be used to explore aspects of the intervention implementation, and they will be measured only in the intervention hospitals.

Clinical data will be collected in four periods, and each will be 1 year apart (Table 4):

  • Period I. Baseline data collection: before randomization in the preparatory phase, for primary and secondary outcomes.

  • Period II. Mid-intervention data collection: immediately before the implementation of the guidelines, for primary outcomes only.

  • Period III. Main post-intervention data collection: immediately following the maintenance component of the intervention, for primary and secondary outcomes.

  • Period IV. Second post-intervention data collection: 1 year after the main post-intervention data collection, for primary outcomes only.

Data from period I (baseline) and III will be used for the primary analyses, and include both primary and secondary outcomes. Secondary outcomes include nonroutine procedures to measure blood loss (see below). Data collection II will be used to study trends and will be limited to primary outcomes, which can be measured without interference with the clinical processes. Data collection IV will be used to measure the sustainability of the results after the end of the intervention and will also be limited to primary outcomes to avoid interference with the clinical processes.

Table 4. Schedule for data collection.

Chart showing outcome assessment timing

(CLAP Trial - go to protocol)

go to protocol )

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Illustrative example - ISAT trial

ISAT [International Subarachnoid Aneurysm Trial] treatment plan:

Assessment at discharge by the local trial coordinator recording key data concerning the patient including the WFNS grade [quality of life index] at time of discharge from neurosurgical unit, length of stay, adverse events and ITU time.

Two month follow-up patient questionnaires will be handed or mailed to the patient by the local co-ordinator.  This is to establish early outcome data.  Outcome assessment will be collected on the Glasgow Outcome Scale, the Rankin  Scale, the Oxford Handicap scale and EuroQol.

Neruopsychological assessment will be made at one year in some centres.

One year follow-up will be conducted by mailing of a postal questionnaire to known surviving patients and relatives at one year after randomisation.  … These questionnaires will collect Glasgow Outcome Scale, Rankin, Oxford Handicap scale and EuroQol.  

(ISAT Trial - go to protocol)


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Additional resources

Trial Protocol Tool resource icon Guidelines and checklist for inclusion of quality of life assessment in clinical trial protocols.

(permission is being sought to include this resource)

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Web resource icon UK Clearing house information sheet on ‘Clarifying desired outcomes’

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Web resource icon UK Clearing House on Health Outcomes

This site was set up to provide information and advice on outcome measures and outcome measurement (primarily directed towards UK NHS but uses generic measures). Provides guidance on selecting outcomes measures and on current literature.

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This page was last updated 4th June 2004.