Covid-19 pandemic as a natural experiment: The case of home advantage in sports

Establishing a causal relationship requires not only the presence of a factor of interest but also the demonstration that the relationship is absent when the factor is absent. Such ideal conditions are rare, especially in observational studies in which creating control conditions is inherently difficult. The COVID-19 pandemic, with its unparalleled disruptions, offers a unique opportunity to isolate causal effects and test previously impossible hypotheses. Here, we examine the home advantage (HA) in sports—a phenomenon in which teams generally perform better in front of their home fans—and how the pandemic-induced absence of fans offered a fortunate yet systematic change to typical conditions, serving as a natural experiment. Using a structural equation modeling approach and building a mediation model encompassing all relevant HA factors, we quantified the reduction in HA and elucidated the specific mechanisms behind it. The theory behind HA and the availability of measures for each factor before and during COVID-19 lockdowns enabled us to estimate all postulated pathways within a natural experimental context. The robust statistical framework used in our study offers a foundational model for integrating naturally occurring events that serve as control conditions into the analysis of various real-life phenomena.