The natural history group is often referred to as the third arm of a controlled drug trial, from the simple notion that a trial has three arms.
The observed outcomes within this group are then compared with the outcomes manifested by a group that has been given the active drug, and with that manifested by a second group who have been given a dummy, placebo drug (thus, the natural history group is the trial's "third arm").
Read more about this topic: Natural History Group
Famous quotes containing the word arm:
“I dreamed of an out-thrust arm of land
Where gulls blew over a wave
That fell along miles of sand....”
—Philip Larkin (1922–1986)
“the uncomfortable angels that rot
On the slabs, a wing chipped here, an arm there:
The brute curiosity of an angel’s stare
Turns you, like them, to stone....”
—Allen Tate (1899–1979)