| estimate_rel_sb {psychmeta} | R Documentation |
Spearman-Brown prophecy formula to estimate the reliability of a lengthened measure
Description
This function implements the Spearman-Brown prophecy formula for estimating the reliability of a lengthened (or shortened) measure. The formula implemented here assumes that all items added to (or subtracted from) the measure will be parallel forms of the original items.
Usage
estimate_rel_sb(rel_initial, k)
Arguments
rel_initial |
Initial reliability of a measure. |
k |
The number of times by which the measure should be lengthened (if k > 1) or shortened (if k < 1), assuming that all new items are parallel forms of initial items. |
Details
This is computed as:
\rho_{XX}^{*}=\frac{k\rho_{XX}}{1+(k-1)\rho_{XX}}
where \rho_{XX} is the initial reliability, k is the multiplier by which the measure is to be lengthened (or shortened), and \rho_{XX}^{*} is the predicted reliability of a measure with a different length.
Value
The estimated reliability of the lengthened (or shortened) measure.
References
Ghiselli, E. E., Campbell, J. P., & Zedeck, S. (1981). Measurement theory for the behavioral sciences. San Francisco, CA: Freeman. p. 232.
Examples
## Double the length of a measure with an initial reliability of .7
estimate_rel_sb(rel_initial = .7, k = 2)
## Halve the length of a measure with an initial reliability of .9
estimate_rel_sb(rel_initial = .9, k = .5)