Answer :
Final answer:
Random assignment is the preferred method for forming test groups in experiments as it minimizes bias and ensures groups are similar except for the treatment being studied.
Explanation:
Random assignment would be more likely used by the researcher to form the test groups for the experiment comparing UV light therapy and oral supplements for treating vitamin D deficiency in older adults. Random assignment ensures that participants are assigned to groups by chance, minimizing the potential for bias. It helps in creating groups that are similar on all characteristics except the treatment being studied.
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