Do ports grow like firms? Gibrat's law, the scaling of growth volatility and rank mobility at 2,065 world ports, 2019–2025
Limanlar firmalar gibi mi büyür? 2.065 dünya limanında Gibrat yasası, büyüme oynaklığının ölçeklenmesi ve sıra hareketliliği, 2019–2025
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Abstract
The debate on whether port systems concentrate rests on the question of whether growth depends on port size. This study tests three regularities from the literature on firm and city growth for world ports: the independence of growth from size (Gibrat's law), the scaling of growth volatility with size, and the distribution of growth rates. Using daily estimates of port calls and cargo derived from satellite-based ship tracking, 5.9 million port-days at 2,065 ports over 2019–2025 are examined. To remove the spurious mean reversion caused by measurement error in size, days are split into two interleaved half-samples; size is measured from one half and growth from the other. The elasticity of growth with respect to size is −0.008 (standard error 0.002): a port ten times larger grows about 1.9 percentage points more slowly per year. The departure is statistically significant but small; it is two fifths of the value found when size and growth are measured from the same half-sample (−0.021), the remainder being measurement error. The standard deviation of growth rates declines with size with an exponent of −0.23 (95% confidence interval 0.21–0.25), clearly below the value of 0.5 expected for a sum of independent units and close to the range reported for firms. Growth rates follow a fat-tailed distribution close to the Laplace rather than the normal. The size distribution is close to lognormal in the body and thinner than lognormal among the largest ports. Ranks are highly persistent: 88% of the hundred largest ports of 2019 are still in the top hundred in 2025. The findings indicate that ports share the statistical growth regularities of firms and that there is no marked tendency towards concentration or deconcentration in the global port system.
Keywords
Port growth; Gibrat's law; Volatility scaling; Laplace distribution; Size distribution; Port concentration; Ship-tracking data
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