A third challenge was how to gather sufficient disaggregated data about the number of children deprived of liberty in order to arrive at scientifically sound global estimates for the different situations covered by the Global Study. In February 2018, we sent out a carefully drafted questionnaire to all States, National Human Rights Institutions, National Preventive Mechanisms, to relevant UN agencies, Non-Governmental Organisations and other stakeholders. We asked them to count all children deprived of liberty at a specific snapshot date (26 June 2018) and to collect annual data, as far as available, for the last 10 years. We received a total of 118 replies from 92 countries, including 67 official State responses. In addition, we collected many more data from official governmental and UN statistics, peer-reviewed literature and other reliable sources and fed them into a specific database created for the Global Study.5 The data collected are sufficient to make statistical extrapolations and to arrive at scientifically sound global estimates. However, all numbers used in the Global Study are highly conservative estimates, and the real numbers are certainly much higher. There is an urgent need for States and their statistical offices to collect data on the total number of children deprived of liberty on a regular basis and for the United Nations to maintain a comprehensive database, which will allow the assessment of trends. Only if we can read from statistics that diversion, deinstitutionalisation and other non-custodial solutions are more effective and less costly than detention to serve the purpose of preventing crime and providing care and protection to children, will States become more eager to follow others in sharply reducing the number of children deprived of liberty. This Global Study is only a first step to draw the attention of States and the international community to a phenomenon that has largely been ignored in the past: that millions of children of all ages are suffering in many different types of detention in violation of international law, and that we are depriving these children of their childhood and of their future. Depriving children of liberty means to expose them to a form of structural violence, while States have committed themselves in the Agenda 2030 to end all forms of violence against children.6 I sincerely hope that this Global Study, which is in need of a comprehensive follow up by States, UN agencies, civil society and others, will contribute to the ultimate goal of the Agenda 2030 to leave no one behind and, in particular, to leave no child behind bars. 5 For the methodology and use of data see, Chapters 2 & 3. 6 See United Nations, Transforming our world: the 2030 Agenda for Sustainable Development, A/RES/70/1, 21 October 2015, Goal 16.2, Available at https://sustainabledevelopment.un.org/content/documents/21252030%20Agenda%20for%20Sustainable%20 Development%20web.pdf (accessed 16 September 2019). 13