Author comment: Limited knowledge of national plastics policy effectiveness may hinder global progress — R0/PR1

Policy effectiveness is a critical measure for assessing whether policies are working and determining necessary adjustments. However, understanding the effectiveness of plastic policies is a significant gap in the toolkit driving solutions to the plastics crisis. This review examines effectiveness evaluations and existing tools for assessing policy effectiveness. The review further identifies the barriers to understanding effectiveness before proposing ways forward. Most studies focus on plastic bag bans or taxes, neglecting other policy instruments. Additionally, these studies often employ simple attribution approaches, rather than causal inference methods, limiting our ability to determine the true impact of policies on desired outcomes. The lack of monitoring and evaluation of plastic policies further hampers knowledge acquisition. The global understanding of the plastics economy and measurable success metrics is insufficient, hindering the design of systemic interventions. These findings highlight the development and evaluation of plastic policies with limited information. A more nuanced understanding of effective plastic policies is necessary, including a harmonised approach to evaluations, a shared definition of effectiveness, the use of rapid assessment tools and the integration of monitoring and evaluation into policy instruments.