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The term natural history group refers to subjects in a drug trial that receive no treatment of any kind and whose illness is, as a consequence, left to run its "natural" course. The term stems from the natural history of an illness, which is the course and outcome of that illness in the absence of treatment.

[edit] First usage

In 1863, Austin Flint (1812–1886) in his report of the first-ever trial that directly compared the efficacy of a placebo treatment with that of an active treatment, spoke of "the natural history of [an untreated] disease".^[1]

[edit] Third arm

The natural history group is often referred to as the third arm of a controlled drug trial, from the simple notion that a triad has three arms (or a triskelion has three legs).

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").

[edit] Notes

1. ^ Flint (1863), p.18.

[edit] References

• Flint, A., "A Contribution Toward the Natural History of Articular Rheumatism, Consisting of a Report of Thirteen Cases Treated Solely with Palliative Measures", American Journal of Medical Science, Vol.46, (July 1863), pp.17-36.

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