1. Validity: Giá trị.  The degree to which output reflects what it purports to reflect, i.e., input; the degree to which output is a function of known input and it alone. For example, does an essay examination validly measure a student’s knowledge of material, or is it invalid, actually measuring his literary skill or the state of the grader’s digestion?

2. Reliability: Độ tin cậy. The degree to which the input-output relationship is reproducible if the relationship is studied repeatedly under comparable conditions. For example, if a student took the same examination twice, or in two forms, would he get the same grade both times? If the same work were reviewed by two graders, would they both assign the same mark?

3. Sensitivity: Độ nhạy. The lowest value of input that can be inferred with a given degree of validity and reliability from measurements of output. Analogous to the usage for the word “threshold” is the phrase “threshold dose”. The engineer uses the word “threshold”, however, to mean the smallest change in input that will result in change in output.

4. Amplification The amount of change in measured output per unit change in input. The slope of the input-output, or dose-effect, curve. (Engineers sometimes refer to “amplification” as “sensitivity”.)

5. Precision The capacity of the system to discriminate between different values of input; the “fineness” with which different values for input can be inferred from measured values of output. The pooled deviation of observed from expected values of output, all divided by the amplification, yields the “index of precision”. The square of the reciprocal of the index of precision is the measure of the amount of information that can be delivered by the system.

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