Hierarchical structure of the European countries based on debts as a percentage of GDP during the 2000–2011 period

•The relationships between countries based on the debts of countries are studied.•We constructed networks by using hierarchical structure methods.•We carried out bootstrap technique to determine the reliability of the links.•We used average linkage cluster analysis to observe cluster structures more clearly.•The less and most affected countries by the debt crisis are formed as a cluster.

We investigate hierarchical structures of the European countries by using debt as a percentage of Gross Domestic Product (GDP) of the countries as they change over a certain period of time. We obtain the topological properties among the countries based on debt as a percentage of GDP of European countries over the period 2000–2011 by using the concept of hierarchical structure methods (minimal spanning tree, (MST) and hierarchical tree, (HT)). This period is also divided into two sub-periods related to 2004 enlargement of the European Union, namely 2000–2004 and 2005–2011, in order to test various time-window and observe the temporal evolution. The bootstrap techniques is applied to see a value of statistical reliability of the links of the MSTs and HTs. The clustering linkage procedure is also used to observe the cluster structure more clearly. From the structural topologies of these trees, we identify different clusters of countries according to their level of debts. Our results show that by the debt crisis, the less and most affected Eurozone’s economies are formed as a cluster with each other in the MSTs and hierarchical trees.