The Living Planet Index (LPI) is a standardized indicator for tracking population trends through time. Due to its ability to aggregate many time series in a single metric, the LPI has been proposed as an indicator for the Convention on Biological Diversity’s post-2020 Global Biodiversity Strategy. However, here we show that random population fluctuations introduce biases when calculating the LPI. By combining simulated and empirical data, we show how random fluctuations lead to a declining LPI even when overall population trends are stable and imprecise estimates of the LPI when populations increase or decrease nonlinearly. We applied randomization null models that demonstrate how random fluctuations exaggerate declines in the global LPI by 9.6%. Our results confirm substantial declines in the LPI but highlight sources of uncertainty in quantitative estimates. Randomization null models are useful for presenting uncertainty around indicators of progress towards international biodiversity targets.

地球生命力指数 (LPI) 是跟踪人口随时间变化趋势的标准化指标。由于 LPI 能够将多个时间序列汇总到一个指标中，因此它被提议作为生物多样性公约 2020 年后全球生物多样性战略的指标。然而，我们在这里表明，随机群体波动在计算 LPI 时会引入偏差。通过结合模拟和经验数据，我们展示了即使总体人口趋势稳定，随机波动如何导致 LPI 下降，以及当人口非线性增加或减少时 LPI 的不精确估计。我们应用随机化零模型来演示随机波动如何使全球 LPI 下降 9.6%。我们的结果证实了 LPI 大幅下降，但强调了定量估计中的不确定性来源。随机零模型对于呈现国际生物多样性目标进展指标的不确定性很有用。