Spearman-Brown formula

Spearman-Brown formula

spearmanBrown(nrOfItems, itemReliability)

spearmanBrown_reversed(nrOfItems, scaleReliability)

spearmanBrown_requiredLength(scaleReliability, itemReliability)

Arguments

nrOfItems

Number of items (or 'subtests') in the scale (or 'test').

itemReliability

The reliability of one item (or 'subtest').

scaleReliability

The reliability of the scale (or, desired reliability of the scale).

Value

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.

Examples

spearmanBrown(10, .4);
#> [1] 0.8695652
spearmanBrown_reversed(10, .87);
#> [1] 0.4009217
spearmanBrown_requiredLength(.87, .4);
#> [1] 10.03846