A controlled experiment is characterized by which statement?

A controlled experiment is characterized by which statement?

• A. The conditions are changed randomly in every trial
• B. The independent variable is not measured
• C. The dependent variable is kept constant
• D. All conditions except the manipulated ones are kept constant

Answer: (D)

In a controlled experiment, the key idea is to isolate the effect of one factor by keeping all other potential influences the same across all trials. By holding every condition constant except the variable you deliberately change, any difference you observe in the outcome can be attributed to that manipulation. That’s why the statement that all conditions except the manipulated ones are kept constant is the best description. For example, if you’re testing how fertilizer amount affects plant growth, you’d keep sunlight, water, soil type, pot size, and other conditions identical for every plant, and vary only the fertilizer level. Then you’d measure growth to see the effect of fertilizer. The other ideas don’t fit the concept: changing conditions randomly would introduce uncontrolled variation and confound the results, making it hard to tell what caused any changes; the independent variable is not measured contradicts the idea of testing its effect; keeping the dependent variable constant would hide any real response to the manipulation.

In a controlled experiment, the key idea is to isolate the effect of one factor by keeping all other potential influences the same across all trials. By holding every condition constant except the variable you deliberately change, any difference you observe in the outcome can be attributed to that manipulation. That’s why the statement that all conditions except the manipulated ones are kept constant is the best description.

For example, if you’re testing how fertilizer amount affects plant growth, you’d keep sunlight, water, soil type, pot size, and other conditions identical for every plant, and vary only the fertilizer level. Then you’d measure growth to see the effect of fertilizer.

The other ideas don’t fit the concept: changing conditions randomly would introduce uncontrolled variation and confound the results, making it hard to tell what caused any changes; the independent variable is not measured contradicts the idea of testing its effect; keeping the dependent variable constant would hide any real response to the manipulation.