手法を比較

	2母数ロジスティックIRTモデル（2PL）	クロンバックのα（信頼性分析）
分野	心理測定学	統計学
系統	Latent structure	Latent structure
提唱年	1980	1951
提唱者	Frederic M. Lord	Lee J. Cronbach
種類	Item response model / latent trait model	Reliability / internal consistency coefficient
原典	Lord, F. M. (1980). Applications of Item Response Theory to Practical Testing Problems. Erlbaum.	Cronbach, L. J. (1951). Coefficient alpha and the internal structure of tests. Psychometrika, 16(3), 297–334.
別名	two-parameter logistic model, 2PL model, 2PL IRT — İki Parametreli Madde Tepki Modeli	coefficient alpha, alpha reliability, internal consistency reliability, Güvenilirlik Analizi (Cronbach Alpha)
関連	6	4
概要	The two-parameter logistic item response model, formalised by Frederic Lord (1980), describes the probability that a respondent answers a binary test item correctly as a smooth S-shaped function of the respondent's latent ability. By estimating a separate discrimination parameter for each item alongside a difficulty parameter, 2PL allows items to differ in how sharply they distinguish high- from low-ability respondents — making it the standard model for large-scale educational and psychological assessments.	Cronbach's alpha is a coefficient of internal consistency that quantifies the degree to which a set of items on a scale measures the same underlying construct. Introduced by Lee J. Cronbach in 1951, it remains the most widely reported reliability index in social-science, health, and educational research.