© Paul Cooijmans


Robustness is the extent to which a test is resistant to score inflation over time. It is based on the reversed correlation between the chronological ranks and the scores of the test submissions. When chronological ranks are not known, another time indicator may be used, such as numbering the months from a given point in the past (e.g. January 1995 = 1, et cetera) and using the month numbers of the test submissions. The latter method may actually be better than the first, as it uses regular time intervals. Robustness is computed thus:

Robustness = √(rscores × time indicators × -1 + 1) / √2

Higher numbers mean greater robustness, and a value of .71 means the scores are perfectly stable over time. Lower values mean the scores are rising over time, higher values (than .71) mean the scores are descending over time.

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