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| Scott's Pi× | Krippendorff's Alpha× | |
|---|---|---|
| Field | Communication | Communication |
| Family | Process / pipeline | Process / pipeline |
| Year of origin≠ | 1955 | 1970 |
| Originator≠ | William A. Scott | Klaus Krippendorff |
| Type≠ | Chance-corrected agreement coefficient for two coders on nominal scales | Chance-corrected reliability coefficient for coded data |
| Seminal source≠ | Scott, W. A. (1955). Reliability of content analysis: The case of nominal scale coding. Public Opinion Quarterly, 19(3), 321–325. DOI ↗ | 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. DOI ↗ |
| Aliases | Scott pi, Scott's index of reliability, Pi reliability coefficient, Scott Pi Katsayısı | Krippendorff alpha, K-alpha, Alpha reliability coefficient, Krippendorff Alfa Katsayısı |
| Related | 4 | 4 |
| Summary≠ | 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. |
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