Webster's New World Medical Dictionary

361
random mating
19_189283 ch18.qxp 4/18/08 10:18 PM Page 361
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occurs, but the concept is important in population
genetics. Also known as panmixus.
random sample
A test group that is selected
solely by chance.
range
In medicine and statistics, the difference
between the lowest and highest numeric values. For
example, if five premature infants are born, weigh-
ing 2, 3, 4, 5, and 6 pounds, respectively, the range
of their birth weights is 2 to 6 pounds.
range, normal
See 
normal range.
range of motion
The full movement potential of
a joint, usually its range of flexion and extension.
For example, a knee might lack 10 degrees of full
extension due to an injury.
rapid eye movement sleep
See 
REM sleep.
rash
Breaking out (eruption) of the skin. A rash
can be caused by an underlying medical condition,
hormonal cycles, allergies, or contact with irritating
substances. Treatment depends on the underlying
cause of the rash. Medically, a rash is referred to as
an exanthem.
Rasmussen syndrome
A rare brain disorder
that is caused by inflammation of brain cells in one
hemisphere. Rasmussen syndrome, whose cause is
unknown, features seizures that can be difficult or
impossible to control with medication, and it even-
tually results in brain shrinkage (atrophy).
Treatment is surgery, if possible. The inflammation
seems to stop of its own accord eventually, but the
damage done is irreversible.
RAST
Radioallergosorbent test, an allergy test that
is done on a sample of blood. RAST is used to check
for allergic sensitivity to specific substances.