The Public Expenditure Efficiency Index (EDP), or Marginal Value of Public Funds (MVPF), is an indicator used to evaluate public policies which compares the benefit derived by the target population – measured by their willingness to pay – to the net cost borne by the public purse. Formalised by Hendren and Sprung-Keyser (2020), it enables very diverse policy interventions – such as transfers, tax credits, education, healthcare and training – to be compared on a single scale. Its denominator comprises direct expenditure and fiscal externalities, i.e. the effects of behavioural responses on future public revenue and expenditure. A ratio greater than 1 indicates a policy that creates more value than it costs; when the net cost is zero, the policy is self-financing and the index tends towards infinity.