Social scientists often seek to understand the relationship between micro social mechanisms and macro social output. In the context of social networks, different micro social mechanisms are usually operationalized by local network mechanisms, while macro social outputs are operationalized by global network structures (Stadtfeld, 2018). Therefore, the aim of this dissertation is to study the relationship between local network mechanisms and global network structures. Not only is the emergence of the selected global network structures addressed, but so too is the transition from one global network structure to another.
A blockmodel is used to define a global network structure. A blockmodel is defined as a network in which the nodes represent clusters of equivalent nodes (according to the structure of their links) from the studied network, while the links in a blockmodel represent the relationships between and within the clusters. The term “block” refers to a submatrix in an adjacency matrix that shows the relationships between nodes from two different clusters or between nodes from the same cluster (Doreian, Batagelj, & Ferligoj, 2005).
Moreover, the social (network) mechanisms can be defined in different ways. Common to the various definitions is the claim that social mechanisms hold an important explanatory role (Hedström & Swedberg, 1998). Stadtfeld (2018) and Hedström & Swedberg (1998) defined three types of mechanisms: situational mechanisms (related to the global network structure’s impact on, e.g. the beliefs, desires and opportunities of an individual), action-formation mechanisms (associated with the impact of individuals’ beliefs, desires and opportunities on their actions/behaviour) and transformational mechanisms (related to the impact of individuals’ actions on the global network structure). In this study, the main focus is given to the last two types of local network mechanisms.
The dissertation consists of two parts. The ability to generate networks with the selected blockmodel types, by considering only the triad types, is addressed in the first part. This research question is especially important because there is no known systematic study addressing a relationship between different triad types and blockmodels as the operationalization of global network structures. Whether the selected blockmodel types can be generated by considering only the triad types without any nodes’ attributes shows that these blockmodels can emerge as a consequence of local network mechanisms such as popularity, assortativity and others.
To study the mentioned research question, different triad types are classified in the set of allowed and the set of forbidden triad types for each blockmodel type that is considered. A given triad type is called ‘allowed’ if its frequency in a given ideal blockmodel is higher than 0; otherwise, it is called ‘forbidden’. The proposed Relocating Links algorithm (RL algorithm) and the Markov Chain Monte Carlo algorithm (MCMC algorithm) are used to generate networks. In general, most studied blockmodels can be generated by only considering different triad types. This shows that some global network structures can emerge by virtue of the local network mechanisms that does not include the nodes’ attributes.
The second part of the dissertation considers local network mechanisms, instead of local network structures, in the context of different blockmodel types. The local network mechanisms are processes that drive the specific actions of the nodes in the network, as described above. Different local network mechanisms are operationalized using different network statistics, which are considered by the nodes, when they obtain an opportunity to change the status of their links. This is done by different proposed algorithms from the NEM family.
Given that there are many possible blockmodel types and possible local network mechanisms, the social context of the study is taken into account to select the most relevant blockmodel types and corresponding local network mechanisms. Two such social contexts considered in this dissertation are: (i) friendships and likings among pre-schoolers; and (ii) the flow of knowledge among employees of an international, knowledge-based company. Based on these two social contexts, two blockmodel types are proposed: an (symmetric and asymmetric) core-cohesive blockmodel, and a hierarchical-cohesive blockmodel with last non-cohesive group. It is shown that the symmetric core-cohesive blockmodel type and the hierarchical-cohesive blockmodel with the last non-cohesive group are appropriate to be considered in the social context relating to a kindergarten and a company.
The results of the Monte Carlo simulations show that the symmetric and asymmetric core-cohesive blockmodel types can emerge due to the mutuality, popularity, assortativity (of in-degree) and transitivity-related local network mechanisms when the initial global network structure is an empty network, a network with a cohesive blockmodel, or a network with an asymmetric core-periphery blockmodel.
It was also shown (based on empirical data collected within a larger longitudinal study in the USA) that the symmetric core-cohesive blockmodel type appears in interactional networks among pre-schoolers. The fact this blockmodel type can be generated by the selected local network mechanisms does not imply that the global network structures of the empirical networks emerged due to the studied local network mechanisms. However, the appearance of this blockmodel type in the empirical data raises some very important developmental questions, which should be answered by considering the nodes’ attributes.
A hierarchical-cohesive blockmodel with the last non-cohesive group can emerge as a result of so-called value-related mechanisms and cost-related mechanisms. Value and cost are defined through the ego's perception of the costs of obtaining the alter's knowledge and the value of the knowledge so obtained (Nebus, 2006). The ability to generate the global network structure, with local network mechanisms that do not consider the nodes’ attributes (except tenure), indicates that a company can develop policies that lead a knowledge flow towards the desired global structure (if it has one).
The most important contribution of this dissertation is the observation that the most common blockmodel types can be generated by the basic local network mechanisms, without taking the attributes of the nodes into account. However, it is necessary to consider the social context and corresponding constraints on the nodes’ characteristics and their behaviour (Doreian & Conti, 2012) while analysing evolution of the global network in real networks.