In the Corruption Perceptions Index which ranks countries by "perceived levels of public sector corruption", Singapore has consistently ranked as one of the least corrupt. Singapore's unique combination of a strong almost authoritarian government with an emphasis on meritocracy and good governance is known as the "Singapore model", and is regarded as a key factor behind Singapore's political stability, economic growth, and harmonious social order. In 2019, the World Justice Project's Rule of Law Index ranked Singapore as 13th overall among the world's 126 countries for adherence to the rule of law. Singapore ranked high on the factors of order and security (#1), absence of corruption (#3), regulatory enforcement (#3), civil justice (#5), and criminal justice (#6), and ranked significantly lower on factors of open government (#25), constraints on government powers (#27), and fundamental rights (#30). All public gatherings of five or more people require police permits, and protests may legally be held only at the Speakers' Corner.