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help for ^sbrowni^
by Herve M. CACI, August 1998
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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@


