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| Gwet's AC1× | Scott's Pi× | |
|---|---|---|
| Field | Communication | Communication |
| Family | Process / pipeline | Process / pipeline |
| Year of origin≠ | 2008 | 1955 |
| Originator≠ | Kilem L. Gwet | William A. Scott |
| Type≠ | Chance-corrected agreement coefficient robust to the prevalence paradox | Chance-corrected agreement coefficient for two coders on nominal scales |
| Seminal source≠ | Gwet, K. L. (2008). Computing inter-rater reliability and its variance in the presence of high agreement. British Journal of Mathematical and Statistical Psychology, 61(1), 29–48. DOI ↗ | Scott, W. A. (1955). Reliability of content analysis: The case of nominal scale coding. Public Opinion Quarterly, 19(3), 321–325. DOI ↗ |
| Aliases | Gwet AC1, AC1 coefficient, Gwet's first-order agreement coefficient, Gwet AC1 Katsayısı | Scott pi, Scott's index of reliability, Pi reliability coefficient, Scott Pi Katsayısı |
| Related | 4 | 4 |
| Summary≠ | Gwet's AC1 is a chance-corrected agreement coefficient introduced by Kilem Gwet in 2008 as a robust alternative to Cohen's and Fleiss' kappa. It targets the kappa paradox — the unsettling result where coders agree on the vast majority of units yet kappa is near zero because one category dominates — by estimating chance agreement in a way that does not collapse when category prevalence is extreme. | 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. |
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