GLOSSARY
OF TERMS
     
     
T
Therapeutic
trial
See clinical
trial.
Trend
- Used
loosely to refer to an association or possible effect that
is not statistically significant.
- A
consistent movement across ordered categories; e.g. a change
in the effect observed in studies grouped according
to, for instance, intensity of treatment.
Trials
register
In
the Cochrane Collaboration, this is a database of bibliographic
references to randomized controlled trials and controlled
clinical trials relevant to a Collaborative Review Group or
Field, that is maintained at the editorial base. Software such
as ProCite or Reference Manager is used to manage the database.
Once a relevant report of a trial is identified, it is photocopied,
coded and entered onto the register. Wherever possible,
relevant trial reports are downloaded directly into the register
from an electronic database such as MEDLINE. Information about
unpublished and ongoing trials is also included in trials
registers.
Triple
blind
(synonym: triple masked)
An expression that is sometimes used to indicate that knowledge
of which study participants are in which comparison group is
kept secret from the statistician doing the analysis as well
as from the study participants and investigators (outcome assessors).
See also blinding,
single
blind,
double
blind.
U
Unit
of allocation
The
entity that is assigned to different comparison groups in a
trial. Most commonly, individuals are allocated, but in some
trials people are assigned to the intervention and control groups
in groups to avoid contamination or for convenience; for example,
practices, hospitals or communities can be allocated. See unit
of analysis error.
Unit
of analysis error
In some studies people are allocated in groups instead of
individually (e.g. by practice, by hospital or by community).
Often when this is done the unit of allocation is different
from the unit of analysis, i.e. people are allocated by groups
and analyzed as though they had been allocated individually.
This is sometimes called a unit of analysis error. Effectively,
using individuals as the unit of analysis when groups of people
are allocated increases the power of the studies by increasing
the degrees of freedom. This can result in overly narrow confidence
intervals
and false positive conclusions that the intervention had an
effect when in truth there is greater uncertainty than what
is reflected by the P-value. In the context of a review, it
can result in studies having narrower confidence intervals and
receiving more weight than is appropriate.
V
Validity
(synonym: internal validity)
Validity is the degree to which a result (of a measurement
or study) is likely to be true and free of bias
(systematic errors). Validity has several other meanings,
usually accompanied by a qualifying word or phrase; for example,
in the context of measurement, expressions such as "construct
validity", "content validity" and "criterion
validity" are used. The expression "internal validity"
is sometimes used to distinguish validity (the extent to which
the observed effects are true for the people in a study) from
external validity or generalisability (the extent to which
the effects observed in a study truly reflect what can be expected
in a target population beyond the people included in the study).
See also methodological
quality,
random
error.
Variable
Any
quantity that varies. A factor that can have different values.
Variance
A
measure of the variation shown by a set of observations defined
by the sum of the squares of deviations from the mean, divided
by the number of degrees of freedom in the set of observations.
Venn
diagram
A
pictorial presentation of the extent to which two or more quantities
or concepts are mutually inclusive and mutually exclusive.
W
Washout
period
The
stage in a crossover
trial
when treatment is withdrawn before the second treatment is given.
Washout periods are usually necessary because of the possibility
that the intervention administered first can affect the outcome
variable for some time after treatment ceases. A run-in
period before a trial starts is sometimes called a washout period
if treatments that participants were using before entering the
trial are discontinued.
World
Wide Web (WWW)
A
part of the Internet
with a graphical interface. "Web pages" or "home
pages" are hypertext Markup Language (HTML) documents on
the WWW. Hypertext allows users to jump from one place in a
document to another, from one document to another, and
from one computer on the WWW to another. A connection through
a cable or over the telephone and a Web browser (software program),
such as Netscape or Internet Explorer, are needed to access
and view WWW documents.
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