Flagged observation analyses as a tool for scoping and communication in Integrated Ecosystem Assessments

TL;DR

This paper introduces Flagged observation analyses, a statistical method using structural time series models and Kalman filtering to identify recent data points that deviate from predicted trends, aiding ecosystem assessment and communication.

Contribution

The paper presents a novel statistical procedure for identifying and communicating recent ecosystem changes through flagged observations in time series data.

Findings

Effective identification of flagged observations outside forecast bands.

Ability to detect unexpected trends in recent data.

Practical applications demonstrated with two case studies.

Abstract

We provide a procedure termed Flagged observation analyses that can be applied to all the available time series to help identifying time series that should be prioritized.The statistical procedure first applies a structural time series model including a stochastic trend model to the data to estimate the long-term trend. The model adopts a state space representation, and the trend component is estimated by a Kalman filter algorithm.The algorithm obtains one- or more-years-ahead prediction values using all past information from the data. Thus, depending on the number of years the investigator wants to consider as "the most recent", the expected trend for these years is estimated through the statistical procedure by using only information from the years prior to them.Forecast bands are estimated around the predicted trends for the recent years, and in the final step, an assessment is made on the extent to which observations from the most recent years fall outside these forecast bands. Those that do, may be identified as flagged observations. A procedure is also presented for assessing whether the combined information from all of the most recent observations form a pattern that deviates from the predicted trend and thus represents an unexpected tendency that may be flagged. In addition to form the basis for identifying time series that should be prioritized in an integrated ecosystem assessment, flagged observations can provide the basis for communicating with managers and stakeholders about recent ecosystem change.Applications of the framework are illustrated with two worked examples.