![\"\"](\"https:\/\/www.psyctc.org\/psyctc\/wp-content\/uploads\/2024\/05\/graphic1-1-1024x630.png\")
<\/figure>\n\n\n\nThe formula does make the assumption that the different length instrument would behave the same way which is almost certainly not the case, however, the predictions are probably a sensible guide and the best we can have in the absence of actual empirical data for the other lengths. See my Rblog for a bit more information and shiny app if you want to play with the predictions the formula makes.<\/p>\n\n\n\n
Try also<\/h4>\n\n\n\n
Cronbach’s coefficient alpha
Internal reliability
Reliability<\/p>\n\n\n\n
Chapters<\/h4>\n\n\n\n
The issue of lengths of measures is touched on in Chapter 4 but the formula is not discussed: too geeky!<\/p>\n\n\n\n
Online resources<\/h4>\n\n\n\n
More detail in my Rblog<\/a>: entry here<\/a>. First created 3.v.24.<\/p>\n","protected":false},"excerpt":{"rendered":" Also known as the Spearman-Brown “prediction” or even “correction” formula and apparently there’s an argument that it should be Brown-Spearman, but I’ve never seen it that way round. Details The formula tells you that, if you have the internal reliability of a multi-item measure, what internal reliability, all things being equal, the measure would have … Continue reading Spearman-Brown formula<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","template":"","meta":{"footnotes":""},"doc_category":[18],"glossaries":[],"doc_tag":[],"knowledge_base":[],"class_list":["post-4233","docs","type-docs","status-publish","hentry","doc_category-om-book"],"year_month":"2026-04","word_count":184,"total_views":"1264","reactions":{"happy":"0","normal":"0","sad":"0"},"author_info":{"name":"chris","author_nicename":"chris","author_url":"https:\/\/www.psyctc.org\/psyctc\/author\/chris\/"},"doc_category_info":[{"term_name":"All OM book glossary entries","term_url":"https:\/\/www.psyctc.org\/psyctc\/glossary\/non-knowledgebase\/om-book\/"}],"doc_tag_info":[],"knowledge_base_info":[],"knowledge_base_slug":[],"_links":{"self":[{"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/docs\/4233","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/docs"}],"about":[{"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/types\/docs"}],"author":[{"embeddable":true,"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/comments?post=4233"}],"version-history":[{"count":1,"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/docs\/4233\/revisions"}],"predecessor-version":[{"id":4235,"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/docs\/4233\/revisions\/4235"}],"wp:attachment":[{"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/media?parent=4233"}],"wp:term":[{"taxonomy":"doc_category","embeddable":true,"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/doc_category?post=4233"},{"taxonomy":"glossaries","embeddable":true,"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/glossaries?post=4233"},{"taxonomy":"doc_tag","embeddable":true,"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/doc_tag?post=4233"},{"taxonomy":"knowledge_base","embeddable":true,"href":"https:\/\/www.psyctc.org\/psyctc\/wp-json\/wp\/v2\/knowledge_base?post=4233"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
App in my shiny apps<\/a> which computes the predictions for you here<\/a>.<\/p>\n\n\n\nDates<\/h4>\n\n\n\n