Adherence means sticking to the treatment
prescribed, or allocated in a clinical trial and, if appropriate,
finishing the course.
Adverse events are undesired effects that may or may not be
related to treatment such as dizziness, stomach ache or a rash. A
symptom caused by the treatment is a side effect. Serious adverse
events in trial participants are reported to the national
regulatory authority (MHRA in the UK).
Bias results when a particular design or
analysis is likely to favour a particular outcome and would,
therefore, make those results unreliable. It is important to avoid
bias in health research as it can distort the results and could
lead to unsafe or ineffective treatments being licensed for use, or
useful treatments being overlooked. One way to avoid bias is by
using randomisation and by
‘blinding’ participants and
Blinding means that trial participants do not know which
treatment they are receiving. This helps prevent bias.
Double blinding refers to the participant, their doctor and
researchers running the trial not knowing which treatment is
received by which group until all data have been
Clinical trials are research studies that
compare different treatments and treatment strategies. They test
whether one is better or, at times, at least as good as another. No
matter how promising a new treatment or treatment strategy may
appear, it must go through clinical trials before its benefits and
risks can really be known.
In cross-over trials participants cross over
and follow the same treatment as the other group they are being
compared to after a certain period of time.
Independent data monitoring committees oversee
the progress of trials. They are made up of experts who are
independent from the trial and who examine its findings while the
trial is still recruiting or in follow-up. If they see evidence
that participants are experiencing serious or
effects, or if it emerges that one treatment being compared is
clearly better than the others, they can advise that a trial is
Disease progression refers to the course that
a disease takes over time.
These are clearly-defined criteria of
who is eligible to take part in a study and who is not as given by
criteria and exclusion
criteria of the study.
An epidemiological, or observational, study
examines data on individuals with a specific condition and does not
intervene in their care, as a clinical trial would. Epidemiological
studies examine the effect of certain exposures (e.g. tobacco
smoke, long duration of HIV infection) on health outcomes (e.g.
An ethics committee is a committee made
up of healthcare professionals and lay people which reviews funded
studies in order to ensure that they are ethically conducted. Study
participants cannot be approached about joining a clinical study
until it has been approved by an ethics committee.
The event rate describes the number of people
who experience a particular event (e.g. tumour recurrence) over a
given time period.
A collection of the best available scientific
research currently available about a health condition. This is used
to make decisions about how best to treat and provide care for
individuals with that condition, or to prevent it.
These determine who is not eligible for a
clinical study. For example, many trials exclude women who
are pregnant, or who may become pregnant, to avoid any possible
danger to a baby, and people who are taking a drug that interacts
with the treatment being studied. (See also eligibility
criteria and inclusion
This is an international quality standard for
the conduct of clinical studies. Randomised Clinical Trials are
required by law to conform to GCP.
In some clinical trials the cost of all
aspects of the treatments being compared is examined. This is
particularly important when there is more than one effective
approach to treating a condition.
These clearly indicate who can join a trial,
e.g. the condition and stage of disease they are already at, and
their age. (See also eligibility
criteria and exclusion
Individual participant data (IPD)
meta-analyses tend to use standard systematic review and meta-analysis methods, but also
involve the central collection and analysis of the original data
from all the relevant trials worldwide, rather than just the
published summary statistics.
This refers to a participant in a research
study agreeing to take part of their own free will after being
given all the important facts about that study, and after they have
had the chance to ask questions and have them satisfactorily
answered and understood.
An analysis of trial data which is undertaken
before the end of the trial.
An intervention is a measure which is
introduced and evaluated through a clinical trial with the aim of
improving health. It could be a treatment (e.g. drug A vs. drug B),
a treatment strategy (e.g. a drug vs. a surgical technique), a
different screening approach, or prevention measure.
Meta-analysis is a means of quantitatively combining the results
of several research studies to provide an ‘average’ estimate of the
This is research to improve the methods used
This refers to a trial which is still
recruiting or following up participants. It may also refer to a
trial where the participant knows which treatment (or treatment
strategy) they are receiving, i.e. they are not blinded (see
blinding). This is usually
called an ‘open label’ trial.
In an open label trial, participants and their
doctors know which treatment (or treatment strategy) they are
Outcomes are measures of health, e.g. response
to treatment, occurrence or recurrence of disease, a measure of
A placebo is a dummy treatment that is
designed to be harmless and to have no effect. It looks, smells and
tastes like the treatment being tested, so that trial participants
do not know if they are taking the dummy treatment or the treatment
itself (see blinding).
Prophylaxis is any measure to prevent a health
condition, rather than curing or treating it, such as vaccination
and use of anti-malaria drugs.
A protocol is the plan for a research study.
Protocols need to be approved by an ethics
committee before the study begins to recruit
participants. They provide information on the question being
addressed by the study, the eligibility criteria, and the visit
schedule for trial participants.
As well as measuring the physical effects of a
treatment (for example changes to blood pressure), many trials now
try to assess the impact of treatments on people’s quality of life.
For example, a ‘quality of life’ study might ask about:
- Participant's mood and general sense of
- Whether participants feel more tired than
- Whether participants are managing to do more
things than before
- Whether participants sleep patterns
Randomisation means that a computer will
decide which treatment or treatment strategy a trial participant
will receive. This ensures that each participant has the same
chance of receiving the treatments or strategies being compared and
avoids one treatment being given to someone because they are a
woman, is older or sicker for example. Randomisation ensures that
the groups of people being compared in a trial are as similar as
possible to start with except for the treatment they receive. This
in turn ensures that any differences between these groups are only
due to the treatments being compared.
Randomisation is central to randomised
controlled trials (RCTs) and allows a fair comparison between trial
groups to be made.
Side effects are undesired effects that are
related to a treatment. see Adverse Events.
Systematic reviews collate evidence from all
the research studies relevant to a particular research question,
using explicit and systematic methods in order to minimise bias.
Therefore, they provide an objective and reliable way of reviewing
Trial arm refers to one of the groups to which
trial participants are assigned to in a randomised controlled
trial. The group of people receiving the current standard
of care are usually referred to as the control arm.
Clinical trials are conducted in phases:
- Phase I: aims to test safety and usually
involve a small number of people
- Phase II: aims to evaluate effectiveness, and
usually involve a larger number of people.
- Phase III: aims to compare two or more
treatments or treatment strategies and monitor side effects.
Results from these trials allow drugs to treatment recommendations
being made and drugs licensed.
- Phase IV: are post-marketing studies and
collect further information on use of treatments in clinical
A trial steering committee (TSC) usually
oversees the conduct of a clinical trial and comprises
investigators as well as independent members.
Last Update Date : 7/19/2012