Final answer:
In the 1747 scurvy trial by James Lind, the independent variable was the type of daily supplement, the dependent variable was improvement in scurvy symptoms, the standardized variable was the sailors' diet, and there was no traditional control group present.
Step-by-step explanation:
In James Lind's 1747 clinical trial on scurvy, the independent variable was the type of daily supplement given to the sailors, which varied among the groups. The dependent variable was the presence or absence of improvement in scurvy symptoms following these interventions. The standardized variable was the diet of the sailors, which was kept consistent across all groups except for the supplements.
A control group in Lind's experiment may have been a group that did not receive any additional supplement, serving as a baseline for comparison; however, Lind's trial did not include a traditional control group by modern standards, as every group received some form of supplement.
Lind's experiment was groundbreaking in that it systematically tested the effects of different dietary supplements on health outcomes, paving the way for the discovery that scurvy is caused by a deficiency in vitamin C, although that specific knowledge came much later.