Final answer:
The statement in question is true; observational studies are used when experimental studies are unethical or infeasible, such as in cases where exposing participants to harmful conditions or withholding treatment cannot be justified.
Step-by-step explanation:
The statement 'Observational studies of preventions and treatments are often conducted when experimental studies are unethical or infeasible' is TRUE. Observational studies are research methods where investigators observe subjects and measure variables of interest without assigning an intervention to the subjects. These types of studies are particularly beneficial when experimental studies, which involve manipulating variables to determine causal effects, are not possible due to ethical, practical, or technical reasons. For example, it would be unethical to conduct an experimental study exposing participants to harmful substances or withholding a potentially life-saving treatment to observe its effects. Therefore, researchers rely on observational studies to collect data and infer associations under these circumstances.