Outcome assessment

This section contains the following:


Wherever possible, the results of a pragmatic trial should provide information about the effectiveness of an intervention provided in its usual clinical setting.  As such, the outcomes for a trial should be those that are likely to be meaningful to the different people (e.g. clinicians, policy makers, patients) who may make decisions about the intervention the trial is evaluating.  Endpoints of interest to decision-makers often include: direct clinical measures e.g. mortality; health related quality of life; disease specific measures; and resource use.  Researchers should consider involving consumers when deciding what outcomes matter most to potential participants (see Consumer Involvement ).  For the calculation of the appropriate sample size for a trial (see Sample size justification ), it is also important to categorise one variable as the primary outcome of interest.

Many questionnaires exist for the measurement of disease-specific and health-related quality of life.  Not all, however, have been appropriately validated, and as such the choice of instrument is crucial to the validity of the trial results.  The rationale behind the choice of instruments should, therefore, be outlined.  Researchers should also consider whether the instruments are available, and validated, in all the languages required.

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Things to consider when writing a protocol

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Illustrative example - WHO pre-eclampsia trial

Outcome variables are classified as primary or secondary.  The primary outcomes of the study are selected on the bases of the following: they can be affected by the intervention, represent an important clinical outcome, are recorded routinely by treatment blinded observer and occur frequently to provide sufficient statistical power.  The primary maternal outcome of the trial is pre-eclampsia.

Hypertension is defined as blood pressure greater than or equal to 140mmHg systolic and/or 90mmHg diastolic occurring in two occasions at least four hours to a week apart after the 20th week of pregnancy.  Diastolic blood pressure will be measured at 5th Korotkoff sound, which is the disappearance of the sounds.  Proteinuria is defined if protein in urine is ≥ 300mg in 24 hours urine specimen or corresponding level of 2+ or more on dipstick.  Pre-eclampsia is defined as hypertension associated with proteinuria.    

Maternal secondary outcomes are: early onset pre-eclampsia (pre-eclampsia starting before 32 weeks of gestation), pregnancy induced hypertension (PIH), eclampsia and placental abruption. (WHO Multicentre Randomized Trial of Calcium Supplementation for the Prevention of Pre-eclampsia - go to protocol)

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Illustrative example - CRASH trial

The primary outcome measures are:

  • Death from any cause within two weeks of injury

  • Death or dependence at six months

Long term recovery will be assessed at six months using the Glasgow Outcome Scale (GOS) which assesses disability and handicap in major areas of life.  The GOS will be administered by a postal questionnaire, completed by a patient or carer, or by telephone interviews.  (CRASH Trial - go to protocol)

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Illustrative example - RaPP trial

We have chosen three main outcome measures, reflecting the elements of clinical practice targeted by our intervention [educational outreach visit with audit and feedback, and computerised reminders]:

  • Proportion of prescriptions of other antihypertensives than thiazides to patients who are being prescribed antihypertensive drugs for the first time (Measurement: data drawn from the practice computer-system).

  • The proportion of patients where the level of cardiovascular risk has not been estimated among all those started on antihypertensive or cholesterol lowering treatment (versus a sample not put on treatment). (Method: Physicians are given the names of the patients they have put on treatment and are asked if the cardiovascular risk has been evaluated, and if so: what the level was).

  • Proportion of patients with a recorded level of cholesterol (total or LDL) or hypertension not satisfying the specified treatment goals, among all patients on the corresponding treatment. For cholesterol we have decided to also include patients on secondary prevention therapy since the treatment goals are similar (Measurement: data drawn from the practice computer system).

We will also investigate the following outcomes:

  • The proportion of patients reporting that they were not involved in the decision-making process before drug treatment for hypertension and/or elevated cholesterol was started. (Measurement: questionnaire to patients started on treatment).

Economic analysis

We will record parameters that describe costs related to our intervention:

  • Salary-costs

  • Time spent arranging for appointments at the doctors’ practices

  • Travel expenses in connection with each outreach visit

  • Amount of physician-time spent at each visit

  • Materials

  • Training

  • Other direct expenses related to the implementation of the intervention

(RaPP 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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Trial Protocol Tool resource icon Events checklist

This checklist has been contributed by Dave Sackett, who prepared it for the forthcoming 3rd edition of Clinical Epidemiology; A Basic Science for Answering Questions about Health Care, to be published by Lippincott, Williams & Wilkins in 2005.

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Trial Protocol Tool resource iconEvents text from 3rd edition of Clinical Epidemiology

This text has been contributed by Dave Sackett, who prepared it for the forthcoming 3rd edition of Clinical Epidemiology; A Basic Science for Answering Questions about Health Care, to be published by Lippincott, Williams & Wilkins in 2005.

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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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Web resource icon Links to commonly used general health outcomes instruments: SF36 and EQ5D

SF36 - Measure of general health status. Widely tested in a range of conditions and settings. 

EQ5D (also known as EuroQol) - Measure of health status which generates a single index value for heath status 

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Further reading

Roland M, Torgerson DJ. Understanding controlled trials: what outcomes should be measured?  BMJ 1998; 317: 1075.

Bowling A.  Measuring health: a review of quality of life measurement scales.  Philadelphia, Open University Press, 1991.

Bowling A.  Measuring disease: a review of disease-specific quality of life measurement scales.  Philadelphia, Open University Press, 1995.

Fitzpatrick R, Davey C, Buxton MJ, Jones DR.  Evaluating patient-based outcome measures for use in clinical trials: a review .  Health Technology Assessment 1998, vol 2: No. 14

Brazier J, Deverill M, Green C, Harper R, Booth A.  A review of the use of health status measures in economic evaluation .  Health Technology Assessment 1999, vol 3: No. 9

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This page was last updated 24th October 2004.