Question

observational studies allow scientists to study systems as a whole while observing and recording data. some research questions require that scientists conduct an experimental study. in an experimental study, scientists manipulate variables to understand the relationship between the variables.
what additional factor, which is not a concern in observational studies, must scientists consider when conducting experimental studies on animal or human subjects?
\bigcirc scientists must consider that in order for the study to be published, it must be subjected to peer review.
\bigcirc scientists must consider the ethical ramifications of the study by weighing the benefits of the research against the liability of adverse effects on the subjects.
\bigcirc scientists must consider how to select a test group and a control group, as well as how to determine the independent and the dependent variables to be tested.
\bigcirc scientists must consider the costs and logistics of the study, as well as any incidental expenditures.

Explanation:

1. Analyze Option 1: Peer review for publication is a general requirement for both observational and experimental studies, not unique to experimental studies with animal/human subjects. So this is incorrect.
2. Analyze Option 2: In experimental studies with animal or human subjects, manipulating variables (like giving a treatment) can harm subjects. Ethical considerations (weighing benefits vs. adverse effects) are crucial here and not a primary concern in observational studies (where you just observe, not manipulate). This fits.
3. Analyze Option 3: Selecting test/control groups and variables is part of experimental design but is also relevant in some observational studies (e.g., cohort studies with groups) and is not an "additional factor" unique to experimental studies with subjects in terms of the question's context (ethical vs. design). So incorrect.
4. Analyze Option 4: Costs and logistics are concerns for both observational and experimental studies, not unique to experimental studies with subjects. So incorrect.

Answer:

B. Scientists must consider the ethical ramifications of the study by weighing the benefits of the research against the liability of adverse effects on the subjects.