.- 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@