.- help for ^sbrowni^ by Herve M. CACI, August 1998 .-Spearman-Brown reliability correction for test length -----------------------------------------------------

^sbrowni^ #rel0 #count0 #count1 ^sbrowni^ #rel0 #count0 #rel1

Description -----------

The reliability of a test (Cronbach's alpha or Kuder-Richardson's coefficient in case of dichotomous items) is dependent of the number of items.

This immediate command comes in two forms:

1. If the reliability is known for a test (#rel0) with any particular number of items (#count0), the Spearman-Brown formula can be used to estimate how much the reliability would increase if the number of items were increased to #count1.

2. The converted formula can be used to estimate the number of items required to obtain a particular reliability (#rel1).

Examples --------

Considering an initial reliability of 0.70 in a 20-item test, the estimated reliability of a 60-item test is computed by:

. ^sbrowni^ .70 20 60

Considering an initial reliability of 0.50 in a 20-item test, the estimated number of items to achieve a reliability of 0.80 is computed by:

. ^sbrowni^ .50 20 .80

Also see --------

STB: ^alpha2^ in sg66 (STB-35) ^KR20^ Manual: ^[R] alpha^ On-line: help for @factor@