What do port calls measure? The divergence of call and cargo cycles at container ports and common movement across world ports, 2019–2026
Uğrak sayısı neyi ölçer? Konteyner limanlarında uğrak ve yük döngülerinin ayrışması ve dünya limanlarında ortak hareket, 2019–2026
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Abstract
Port call counts derived from ship-tracking data are increasingly used as a real-time indicator of seaborne trade. This use rests on the assumption that the number of calls moves together with the cargo carried. In this study the assumption is tested with common factors extracted from the monthly activity of world ports. Daily port records are aggregated to monthly totals, global factors are estimated from the year-on-year growth rates of 1,361 ports for January 2020–October 2026, and the significance of the factors is tested against a null distribution that shifts each port's series randomly in time. The assumption holds for non-container ships: the correlation between the growth of calls and of tonnage in the world total is 0.87. It does not hold for container ships: the same correlation is 0.23, and the global factor extracted from container calls is the mirror image of the global factor extracted from container tonnage (correlation −0.81). In 2021 container calls changed by −2.3% while tonnage rose by 4.7%; in 2023 calls rose by 8.7% while tonnage rose by 2.4%. The container call factor is strongly and negatively related to the supply chain pressure index (−0.62) and lags the general port cycle by about a year. The finding shows that in container shipping the number of calls measures the throughput capacity of the system rather than demand. The study also presents a hierarchical variance decomposition of port activity: the global factor explains only 4.2% of variability at the median port, but 49% in the world total.
Keywords
Port calls; Container shipping; Port congestion; Common factor; Real-time trade indicators; Variance decomposition
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