手法を比較

	Scott's Pi	Krippendorff's Alpha
分野	Communication	Communication
系統	Process / pipeline	Process / pipeline
提唱年	1955	1970
提唱者	William A. Scott	Klaus Krippendorff
種類	Chance-corrected agreement coefficient for two coders on nominal scales	Chance-corrected reliability coefficient for coded data
原典	Scott, W. A. (1955). Reliability of content analysis: The case of nominal scale coding. Public Opinion Quarterly, 19(3), 321–325.	Hayes, A. F., & Krippendorff, K. (2007). Answering the call for a standard reliability measure for coding data. Communication Methods and Measures, 1(1), 77–89.
別名	Scott pi, Scott's index of reliability, Pi reliability coefficient, Scott Pi Katsayısı	Krippendorff alpha, K-alpha, Alpha reliability coefficient, Krippendorff Alfa Katsayısı
関連	4	4
概要	Scott's pi is a chance-corrected coefficient of intercoder agreement for two coders working on a nominal scale, introduced by William Scott in 1955 specifically for content analysis. It improves on raw percent agreement by subtracting the agreement two coders would reach by chance, where chance is estimated from a single pooled distribution of categories shared by both coders rather than from each coder's separate marginals.	Krippendorff's alpha is a chance-corrected coefficient that quantifies the reliability of coding decisions made by two or more observers, and is the standard reliability statistic in communication content analysis. Unlike percent agreement, it corrects for the agreement expected by chance; unlike Cohen's kappa, it generalizes seamlessly to any number of coders, any measurement level (nominal, ordinal, interval, ratio), and data sets with missing values.