Causality Relationship Between Nonpharmaceutical Interventions and Coronavirus Disease 2019 in Turkey

Objective: The aim of this study was to investigate the relationship between the level of nonpharmaceutical interventions and 2 major coronavirus disease 2019 (COVID-19) indicators: new confirmed cases of COVID-19 and new deaths from COVID-19 in Turkey. Methods: Daily data from March 11, 2020, to March 8, 2022 were used. First, the number of new cases and new deaths per million and the average of the stringency index for each week were calculated. Then, the Toda and Yamamoto causality analysis was conducted to obtain robust results on the dual causality relationship between the stringency index and 2 major COVID-19 indicators: new COVID-19 cases and deaths. Results: The study results show that an increase in the number of new cases and deaths in weekly data leads to an increase in the stringency level, but the stringency level does not have a significant effect on new cases and deaths in weekly data. However, it was concluded that increases in the stringency level led to a significant COVID-19 incidence reduction in the subsequent 28 days. Conclusion: It can be said that there is a 1-way causal relationship between new COVID-19 cases and deaths in Turkey and the level of nonpharmaceutical interventions for a weekly period. In this context, it is crucial for governments to plan, considering the lagged effect of the stringency index on the number of cases and deaths. The findings may help decision-makers better understand the consequences of the COVID-19 pandemic interventions and determine the appropriate strategies in Turkey and elsewhere. Keywords: COVID-19, containment measures, nonpharmaceutical interventions, stringency index, causality test