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Flashcards in Study Design: Clinical Trials Deck (16):

Define bias

A systematic error in design, conduct or analysis of a study which produces a mistaken estimate of treatment effect


Define confounding

When a variable (or factor) is related to both the study variable and the outcome so the effect of the study variable on the outcome is distorted


What is a clinical trial and why is it unique?

A planned experiment in humans, designed to measure the effectiveness of an intervention. Experimental studies like trials are different from most epidemiological studies (surveys, cross sectional, cohort, case control, ecological) which are observational.


What are some features of a clinical trial?

It must contain a control group, it is prospective- patients followed through time, patients treated and followed over same period of time, patients are randomised, double-blind


What is a control group?

Group that don't receive intervention. " A control group must be included otherwise you cannot be sure why the outcome happened


Why should you randomise?

To remove treatment allocation bias


What are 3 types of randomisation?

Block randomisation, stratification, minimisation


Why should trials be double blind/ blind?

Blinding means that the patient does not know whether they are getting the new treatment or not.

In a double blind trial neither the patient nor the doctor knows which treatment they are getting.

This is to prevent bias in reporting or measurement of the outcome, measurement bias.


All clinical trials must be RRAA

Reviewed by independent scientific committee
Approved by a research ethics committee
Adhere to gov. and international guidelines


How are trial outcomes presented?

In terms of efficacy (the true biological effect of a treatment) or effectiveness (effect of a treatment when actually used in "normal" practice).


What are the trial outputs?

- The experimental event rate (EER) = incidence in the intervention arm
- Control event rate (CER) = incidence in the control arm
Relative risk = EER/CER

- Relative reduction = (CER- EER)/ CER
- Absolute risk reduction (ARR) = CER- EER
- Number needed to treat (NNT) = 1/ARR


What are clinical trials reported according to?

CONSORT guidelines


What happens in phase 1 of a trial?

Aim is to test safety by looking at side effects, small number of people used


What happens in phase 2 of a trial?

Larger group of people tested who have the disease- few hundred. Also looks are safety


What happens in phase 3 of a trial?

Larger group of people from different countries. Comparison of new treatment with treatment currently in use. Efficacy and side effects are observed.


what happens in a phase 4 trial?

Done after drug has been marketed to get info on drug's effect in different populations