spearmanBrown(nrOfItems, itemReliability) spearmanBrown_reversed(nrOfItems, scaleReliability) spearmanBrown_requiredLength(scaleReliability, itemReliability)
Number of items (or 'subtests') in the scale (or 'test').
The reliability of one item (or 'subtest').
The reliability of the scale (or, desired reliability of the scale).
spearmanBrown, the predicted scale reliability; for
the number of items required to achieve the desired scale reliability; and for
the reliability of one item.
spearmanBrown(10, .4); #>  0.8695652 spearmanBrown_reversed(10, .87); #>  0.4009217 spearmanBrown_requiredLength(.87, .4); #>  10.03846