Spearman-Brown formula
spearmanBrown(nrOfItems, itemReliability) spearmanBrown_reversed(nrOfItems, scaleReliability) spearmanBrown_requiredLength(scaleReliability, itemReliability)
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). |
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