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Nous fournissons des preuves et des solutions concrètes pour transformer l’utilisation des terres et la production alimentaire : conserver et restaurer les écosystèmes, répondre aux crises mondiales du climat, de la malnutrition, de la biodiversité et de la désertification. En bref, nous améliorons la vie des populations.

CIFOR-ICRAF publie chaque année plus de 750 publications sur l’agroforesterie, les forêts et le changement climatique, la restauration des paysages, les droits, la politique forestière et bien d’autres sujets encore, et ce dans plusieurs langues. .

CIFOR-ICRAF s’attaque aux défis et aux opportunités locales tout en apportant des solutions aux problèmes mondiaux concernant les forêts, les paysages, les populations et la planète.

Nous fournissons des preuves et des solutions concrètes pour transformer l’utilisation des terres et la production alimentaire : conserver et restaurer les écosystèmes, répondre aux crises mondiales du climat, de la malnutrition, de la biodiversité et de la désertification. En bref, nous améliorons la vie des populations.

CIFOR–ICRAF publishes over 750 publications every year on agroforestry, forests and climate change, landscape restoration, rights, forest policy and much more – in multiple languages.

CIFOR–ICRAF addresses local challenges and opportunities while providing solutions to global problems for forests, landscapes, people and the planet.

We deliver actionable evidence and solutions to transform how land is used and how food is produced: conserving and restoring ecosystems, responding to the global climate, malnutrition, biodiversity and desertification crises. In short, improving people’s lives.

Estimating sample size for inference about the Shannon-Weaver and the Simpson Indices of species diversity

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A framework for a priori estimation of the expected sampling variances of the Shannon-Weaver and the Simpson indices of species diversity is developed by the introduction of the most probable relative species abundance distribution (MOPSAD). MOPSAD gives the prior probability of a species' relative abundance. The beta distribution is used here as the prior for MOPSAD. Sample sizes needed for efficient statistical inference and hypothesis testing about the two indices are provided for 16 distinct beta priors for MOPSAD. Shannon-Weaver and Simpson's diversity indices in plant communities expected to have a `U'-shaped or a J-shaped MOPSAD will have large sampling variances. For the same statistical resolution the Simpson index requires about nine times as many samples as the Shannon-Weaver index. The impact of a positive or negative spatial association among species on the variance of the diversity indices was also assessed. In general, spatial association had little impact on the variance of the indices; it suffices to increase the sample size by about 5% as a safeguard against variance inflation due to spatial associations.

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