| spearman.brown {CTT} | R Documentation |
Functions for Spearman-Brown "Prophecy" Formula
Description
This function calculates either a predicted reliability for a measure given the original reliability and a new test length, or the function calculates the required test length to achieve a desired level of reliability.
Usage
spearman.brown(r.xx, input = 2, n.or.r = "n")
Arguments
r.xx |
The original relibility |
input |
The new test length or a desired level of reliability, depending on n.or.r |
n.or.r |
If n.or.r="n", the function will return a new reliability; if n.or.r="r", the function will return the factor by which the test length must change to achieve a desired level of reliability. |
Details
If n.or.r="n", the function will return a new reliability and input should be the factor by which the test length is to be changed. If n.or.r="r", the function will return the factor by which the test length must change to achieve a desired level of reliability (provided in input).
Author(s)
John Willse, Zhan Shu
References
Spearman, C. (1910). Correlation calculated with faulty data. British Journal of Psychology, 3,
271-295.
Brown,W. (1910). Some experimental results in the correlation of mental abilities. British Journal
of Psychology, 3, 296-322.
Examples
# old relibility is 0.6, if the measure is lengthened
# by a factor of 2, the relibility of new test is:
spearman.brown(0.6,2,"n")
# old relibility is 0.5, if we want a new measure to
# be 0.8, the new test length is:
spearman.brown(0.5, 0.8, "r")