Exercise 1: Identifying the Variables in Lind's Real Trial — Possible Solution
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INDEPENDENT VARIABLE: the specific remedy given to each pair - cider,
elixir of vitriol, vinegar, seawater, a purgative mixture, or oranges
and lemons. This is the variable Lind deliberately changed between the
six groups.

DEPENDENT VARIABLE: the degree of real improvement in each pair's own
scurvy symptoms after six days. This is what Lind measured as the
outcome, to see whether it changed depending on which remedy a pair
received.

CONTROLLED VARIABLES (at least two): (1) disease stage - Lind
specifically selected sailors at similarly early stages of scurvy,
rather than mixing severe and mild cases across groups; (2) basic diet
and shipboard conditions - beyond the specific remedy each pair
received, their general food, environment, and daily routine aboard
the Salisbury stayed the same. A third real controlled variable worth
naming: the six-day trial duration was the same for all pairs, so no
group got more time to potentially improve than another.

ANSWER: Independent variable = the specific remedy (cider, vitriol
elixir, vinegar, seawater, purgative mixture, or citrus). Dependent
variable = the degree of real symptom improvement after six days.
Controlled variables = disease stage at the start, general diet and
shipboard conditions, and the equal six-day duration across all pairs.

WHY THIS WORKS AS AN ANSWER
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This correctly identifies all three variable types using the chapter's
own real trial details, with more than the minimum two controlled
variables named for a fuller, more precise answer.