Clinical trials

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Evaluating a clinical trial F. Javier Rodriguez- Vera Department of Internal Medicine. Hospital do Barlavento Algarvio. Portimão. Portugal. EU

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Page 1: Clinical trials

Evaluating a clinical trial

F. Javier Rodriguez-Vera

Department of Internal Medicine.

Hospital do Barlavento Algarvio.

Portimão. Portugal. EU

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Study designed to answer specific questions about vaccines or new therapies or new ways of using known treatments. Clinical trials (also called medical research or research studies) are used to determine whether new drugs or treatments are both safe and effective

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Once researchers test new therapies or procedures in the laboratory and get promising results, they begin planning clinical trials. New therapies are tested on people only after laboratory and animal studies show promising results.

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Basically, a trial is comparing to options in a situation.

These two options may be




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Depending on the complexity, Trials may be:


Uncontrolled clinical trial

Controlled clinical trial

Randomized controlled trial

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Study Before-after:

Is the simplest and not properly a trial

Consists in comparing the situation in a person or group of people in two points of time: before aplying a certain drug and after doing it

The probability of bias is high

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Uncontrolled clinical trial

An intervention is given

Two groups are compared

The allocation to the groups is not randomized

May happen that the two groups compared are not homogeneous

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Controlled clinical trial

An intervention is done in two groups which have been randomly created

Both the patients and the doctors know the intervention apllied, so there exists Placebo effect

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•An RCT seeks to measure and compare the outcomes of two or more clinical interventions.•One intervention is regarded as the standard of comparison or control.•Participants receive the interventions in random order to ensure similarity of characteristics at the start of the comparison•Randomisation can be achieved through a variety of procedures•Individuals, groups, and the order in which measurements are obtained can all be randomised •RCTs cannot answer all clinical questions

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RCT is a study in which people are allocated at random to receive one of several clinical interventions.

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RCTs are quantitative, comparative, controlled experiments in which a group of investigators studies two or more interventions in a series of individuals who receive them in random order.

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RCTs can be classified according to: (1) the aspect of the interventions investigators want to explore.(2) the way in which the participants are exposed to the

interventions. (3) the number of participants included in the study. (4) whether the investigators and participants know which

intervention is being assessed. (5) whether the preferences of non-randomised individuals and

participants are taken into account in the design of the study.

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Why a clinical trial has to be analyzed? The bias

Any factor or process that tends to deviate the results or conclusions of a trial systematically away from the truth

Bias can occur in a trial during the planning stages, the selection of participants, the administration of interventions, the measurement of outcomes, the analysis of data, the interpretation and reporting of results, and the publication of reports.Bias can also occur when a person is reading the report of a trial.

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Types of bias

Selection biasSelection bias occurs when the outcomes of a trial are affected by systematic differences in the way in which individuals are accepted or rejected for a trial, or in the way in which the interventions are assigned to individuals once they have been accepted into a trial

Ascertainment biasAscertainment bias occurs when the results or conclusions of a trial are systematically distorted by knowledge of which intervention each participant is receiving. Ascertainment bias can be introduced by the person administering the interventions, the person receiving the interventions (the participants), the investigator assessing or analysing the outcomes, and even by the people who write the report describing the trial.

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What is publication bias?Some evidence shows a propensity for investigators and sponsors to write and submit, and for peer-reviewers and editors to accept, manuscripts for publication depending on the direction of the findings

What is language bias?Recently, a variation of publication bias has been described as ‘language bias’, to indicate that manuscripts may be submitted to and published by journals in different languages depending on the direction of their results, with more studies with positive results published in English

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What is country of publication bias?It has also been shown that researchers in some countries may publish only positive results, such as with RCTs evaluating acupuncture conducted in China, Japan, Hong Kong, and Taiwan.

What is time lag bias?This bias occurs when the speed of publication depends on the direction and strength of the trial results.1 In general, it seems that trials with ‘negative’ results take twice as long to be published as ‘positive’ trials.

What is ‘potential breakthrough’ bias?This type of bias can be introduced by journalists (and, increasingly, Internet publishers) if they systematically select, overrate, and disseminate trials depending on the direction of the findings.

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Rivalry bias Underrating the strengths or exaggerating the weaknesses of studies published by a rival.

I owe him one’ bias This is a variation of the previous bias and occurs when a reader (particularly a peer-reviewer) accepts flawed results from a study by someone who did the same for the reader

Personal habit bias Overrating or underrating a study depending on the habits of the reader

Moral bias Overrating or underrating a study depending on how much it agrees or disagrees with the reader's morals

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Clinical practice bias Overrating or underrating a study according to whether the study supports or challenges the reader's current or past clinical practice

It refers to the systematic overrating or underrating of studies that describe complementary medicine interventions, particularly when the results suggest that the interventions are effective

Complementary medicine bias

Do something’ bias Overrating a study which suggests that an intervention is effective, particularly when there is no effective intervention available

‘Do nothing’ bias This bias is related to the previous one. It occurs when readers underrate a study that discourages the use of an intervention in conditions for which no effective treatment exists

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Favoured design bias Overrating a study that uses a design supported, publicly or privately, by the reader

Disfavoured design bias The converse of favoured design bias. It occurs when a study is underrated because it uses a design that is not favoured by the reader Resource allocation bias Overrating or underrating a study according to the reader's preference for resource allocation.

Prestigious journal bias This occurs when the results of studies published in prestigious journals are overrated.

Non-prestigious journal bias The converse of prestigious journal bias. It occurs when the results of studies published in non-prestigious journals are underrated.

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Printed word bias This occurs when a study is overrated because of undue confidence in published data

Prominent author bias This occurs when the results of studies published by prominent authors are overrated.

Unknown or non-prominent author bias. It occurs when the results of studies published by unknown or non-prominent authors are underrated.

Famous institution bias This occurs when the results of studies emanating from famous institutions are overrated.

Unrecognised or non-prestigious institution bias Related to the previous bias. It occurs when the results of studies emanating from unrecognised or non-prestigious institutions are systematically underrated.

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Large trial bias . It occurs when the results of large trials are overrated.

Multicentre trial bias . It occurs when the results of multicentre collaborative trials are overrated. These trials do not necessarily have large sample sizes

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Assessing the quality of RCTs: why, what, how, and by whom?

•There is no such thing as a perfect trial.•Internal validity is an essential component of the assessment of trial quality.•There are many tools to choose from when assessing trial quality, or new ones can be developed.•Using several people to assess trial quality reduces mistakes and the risk of bias during assessments.•How to use quality assessment will depend on your role, the purpose of the assessment, and the number of trials on the same topic being evaluated.•The CONSORT statement aims to improve the standard of written reports of RCTs.

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•Answer clear and relevant clinical questions previously unanswered.•Evaluate all possible interventions for all possible variations of the conditions of interest, in all possible types of patients, in all settings, using all relevant outcome measures.•Include all available patients.•Include strategies to eliminate bias during the administration of the interventions, the evaluation of the outcomes, and reporting of the results, thus reflecting the true effect of the interventions.•Include perfect statistical analyses.•Be described in reports written in clear and unambiguous language, including an exact account of all the events that occurred during the design and course of the trial, as well as individual patient data, and an accurate description of the patients w ho were included, excluded, withdrawn, and dropped out.•Be designed, conducted, and reported by researchers who did not have conflicts of interest.•Follow strict ethical principles.

A good clinical trial

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2a. Were all subjects who entered the trial accounted for at its conclusion?

2b. Were they analyzed in the groups to which they were


Critical appraisal. Treatment.

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3a. Aside from the experimental treatment, were the groups treated equally?

3b. Were the groups similar at the start of the trial?

Critical appraisal. Treatment.

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Is the research important?

RRR (Relative risk reduction)

ARR (Absolute risk reduction)

NNT (Number needed to treat)

Critical appraisal. Treatment.

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Can I apply it to my patient?

4. Is this patient so different from those in the trial that the results don’t apply?

Critical appraisal. Treatment.

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5a. How great would the benefit of therapy be for this particular patient?

5b. What is the event rate in my practice for patients like this one?

Critical appraisal. Treatment.

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Is it consistent with the patients values and preferences?

6. Do I have a clear assessment of the patient’s values and preferences?

Critical appraisal. Treatment.

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7. Do this intervention and its potential consequences meet them?

Critical appraisal. Treatment.

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Critical appraisal. Diagnosis

Is the research valid?

1. Was there an independent, blind comparison with a reference ("gold") standard of diagnosis?

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2. Was the diagnostic test evaluated in an appropriate spectrum of patients (like those in whom it would be used in practice)?

Critical appraisal. Diagnosis

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3. Was the reference standard applied regardless of the diagnostic test result?

Critical appraisal. Diagnosis

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Is the research important?



Critical appraisal. Diagnosis

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Is the research important?



Critical appraisal. Diagnosis

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Can I apply it to my patient?

4. Is the diagnostic test available, affordable, accurate, and precise in your setting?

Critical appraisal. Diagnosis

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5. Can you generate a clinically sensible estimate of your patient's pre-test probability (from practice data, from personal experience, from the report itself, or from clinical speculation?)

Critical appraisal. Diagnosis

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6. Will the resulting post-test probabilities affect your management and help your patient? (Could it move

you across a test-treatment threshold?)

Critical appraisal. Diagnosis

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Critical appraisal. Prognosis/harm

Is the research valid?

1. Was a defined, representative sample of patients assembled at a common (usually early) point in the course of their disease?

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2. Was patient follow-up sufficiently long and complete?

Critical appraisal. Prognosis/harm

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3. Were objective outcome criteria applied in a "blind" fashion?

Critical appraisal. Prognosis/harm

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4. If subgroups with different prognoses are identified, was there adjustment for important prognostic factors?

Critical appraisal. Prognosis/harm

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5. Was there validation in an independent group ("test-set") of patients?

Critical appraisal. Prognosis/harm

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Is the research important?

Outcome Rate (95% CI) Probability (95% CI)

Critical appraisal. Prognosis/harm

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Can I apply it to my patient?

6. Were the study patients similar to your own?

Critical appraisal. Prognosis/harm

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7. Will this evidence make a clinically important impact on your conclusions about what to offer or tell your patient?

Critical appraisal. Prognosis/harm

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After the critical appraisal you conclude that that article you´ve read has a low-moderate-high probabilities to be biased

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