In an experiment the levels of the independent variable were very close and the instrument was not sensitive enough. What outcome is possible?

Correct answer: A real effect may remain undetected

The direct answer is A: a real effect may remain undetected. If two levels of an independent variable are very close, the true change may be smaller than the instrument can reliably distinguish. The reasoning is: make a small change, take a reading, compare it with another reading, and consider the instrument’s resolution and measurement error. If the difference is hidden within that error, the experiment may show little or no visible effect even when an effect exists. A is correct. B is wrong because no result automatically proves causation; controls and sound design are needed. C is wrong because a weak instrument does not become accurate by itself. D is wrong because a control group remains useful for comparison. Memory cue: small effect plus insensitive instrument can mean “not detected,” not “not present.”