Please find one problem with this experimental design from the
point of view of modern statistical theory.
In 1747, while serving as surgeon on HM Bark Salisbury, James
Lind, the ship's surgeon, carried out a controlled experiment to
develop a cure for scurvy.
Lind selected 12 men from the ship, all suffering from scurvy,
and divided them into six pairs, giving each group different
additions to their basic diet for a period of two weeks. The
treatments were all remedies that had been proposed at one
time or another. They were:
- A quart of cider every day
- Twenty five gutts of elixir vitriol three times a day upon an empty stomach,
- One half-pint of seawater every day
- A mixture of garlic, mustard, and horseradish in a lump the size of a nutmeg
- Two spoonfuls of vinegar three times a day
- Two oranges and one lemon every day.
The men who had been given citrus fruits recovered dramatically
within a week. One of them returned to duty after 6 days and the
other became nurse to the rest. The others experienced some
improvement, but nothing was comparable to the citrus fruits,
which were proved to be substantially superior to the other
In this study his subjects' cases "were as similar as I could
have them", that is he provided strict entry requirements to
reduce extraneous variation. The men were paired, which provided