A modified Wilcoxon test for non-negative distributions with a clump of zeros.
Stat Med
; 29(3): 391-400, 2010 Feb 10.
Article
en En
| MEDLINE
| ID: mdl-19941301
Comparing two samples with a continuous non-negative score, e.g. a utility score over [0, 1], with a substantial proportion, say 50 per cent, scoring 0 presents distributional problems for most standard tests. A Wilcoxon rank test can be used, but the large number of ties reduces power. I propose a new test, the Wilcoxon rank-sum test performed after removing an equal (and maximal) number of 0's from each sample. This test recovers much of the power. Compared with a (directional) modification of a two-part test proposed by Lachenbruch, the truncated Wilcoxon has similar power when the non-zero scores are independent of the proportion of zeros, but, unlike the two-part test, the truncated Wilcoxon is relatively unaffected when these processes are dependent.
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Colección:
01-internacional
Base de datos:
MEDLINE
Asunto principal:
Estadísticas no Paramétricas
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Tamaño de la Muestra
Tipo de estudio:
Prognostic_studies
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Risk_factors_studies
Límite:
Humans
Idioma:
En
Revista:
Stat Med
Año:
2010
Tipo del documento:
Article
País de afiliación:
Estados Unidos
Pais de publicación:
Reino Unido