Probing Concepts with a Research-Based Instrument: The Force Concept Inventory (FCI)
David Hestenes and his collaborators have developed an "instrument" (ed jargon) or a "detector" (physics jargon) to probe student's understanding of basic concepts.
The choice of FCI topics is based on careful thought about what the fundamental issues and concepts are in Newtonian dynamics.
The FCI distractors (wrong answers) are malicious -- they are based on research that shows what the students' most common misconceptions are.
The “efficiency”, h, (fraction of the possible gain) appears to yield an appropriate comparative measure.