Spearman-Brown formula
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).
For spearmanBrown
, the predicted scale reliability; for spearmanBrown_requiredLength
,
the number of items required to achieve the desired scale reliability; and for spearmanBrown_reversed
,
the reliability of one item.
spearmanBrown(10, .4);
#> [1] 0.8695652
spearmanBrown_reversed(10, .87);
#> [1] 0.4009217
spearmanBrown_requiredLength(.87, .4);
#> [1] 10.03846