Calculating uncertainty

Calculating uncertainty

Our estimates of BII for a country, region or the world are derived from statistical modelling of the whole data set.

To calculate the uncertainty of these estimates, we fitted the same statistical models ten times, leaving out the data from one major biome (broad natural habitat type) each time, and used these to project BII.

This technique, known as cross-validation, yielded ten estimates and we report the lowest and highest of these as our uncertainty margins at the end of each decade.

The range of estimates can be quite wide, partly because two of the biomes in particular - temperate broadleaf and mixed forests, and tropical and subtropical moist broadleaf forests - are particularly well represented in the data.

Cross-validation commonly leaves out a random subset of the data each time, but that approach underestimates the true uncertainty in parameter estimates.

In the future, we plan to also cross-validate by splitting the data up into major taxonomic groups. 

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External data sets

The Biodiversity Trends Explorer

Indicator: The Biodiversity Intactness Index, accessed through the Biodiversity Trends Explorer

Data set: Available through the NHM Data Portal

Modelling framework: Available through GitHub

Geographical standards used: UN M49 StandardNatural Earth

Related Museum project: PREDICTS

Project and research leads: Professor Andy Purvis and Dr Adriana De Palma

Papers: Hudson et al. 2017Hudson et al. 2016LeClere et al. 2020; and Hill et al. 2018

Data last updated: October 2021