Investigating the persistence degree of environmental patent: application of panel SPSM-quantile unit root test

This article analyzes the degree of persistence of shocks to environmental patents in the OECD countries from 1980 to 2022 by applying the panel quantile unit root (PQUR) test and sequential panel selection (SPS) method. Our results indicate that most OECD countries reveal similar stochastic behaviours, where low and extreme (middle and moderate high) quantiles behave as unit root (stationary) processes. According to our findings, except for the US, the time series of environmental patents of other OECD countries behaved as a unit root process in 2022. Accordingly, the mandatory and incentive pro-green innovation policies have long-lasting effects on the development of the patents.