Description Usage Arguments Details Author(s) References Examples

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.

1 | ```
spearman.brown(r.xx, input = 2, n.or.r = "n")
``` |

`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. |

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).

John Willse, Zhan Shu

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.

1 2 3 4 5 6 7 | ```
# 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")
``` |

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