In an article focused on differentiating the benefits of particular local network positions for strategic performance within a market setting, Podolny (2001) introduced the terms “pipes” and “prisms” to label the two general theoretical means by which networks shape other outcomes. These terms offer tangible metaphors for the two most common underlying mechanisms often at work within network research.
The pipes metaphor accounts for what is likely the most readily apparent network mechanism.9 Thinking of the ties within networks as pipes conveys the notion that networks provide potential pathways through which various “bits” can be passed from one node to another (Morris 1993; Valente and Pitts 2017). Those bits to be transmitted could be diseases spreading through contact networks, ideas flowing through communication networks, or money transfers across a financial market. In these cases, network studies aim to identify properties that promote or constrain the potential transmission of those bits through the population (Valente and Davis 1999). For example, just like in the telephone game you played as a child, the longer the distance that a message must travel, the less likely it is to be successfully transmitted (network distance reduces transmission likelihood). Or if more of the communication within a group must travel through a single party, the more likely that party is to have the ability to shape the opinions of the group (i.e., betweenness centrality increases control over flow through a population). Returning to Figure Figure 1.1 from this perspective, we could explain why node 6 would be more likely to successfully send something to node 5 than to node 1, and why node 9 isn’t likely to receive anything from anyone else.
The prisms metaphor instead suggests that a node’s status can be gleaned from (reflected in) their position with respect to the pattern of relationships surrounding them (Wellman 1988).10 In this orientation, networks shape patterns that reveal differences or similarities in roles between compared nodes. Research employing this metaphor aims to identify patterns of nodes’ locations within networks that meaningfully differentiate between their respective positions (Eguiluz et al. 2005).11 For example, while your aunt is not my aunt, our aunts are related to us in the same way—each is the sister of our respective parents (this is an example of structural equivalence). Or in organizational networks, administrative assistants often have higher levels of communication, because their relationships necessarily span levels within the hierarchy (connecting leaders to members of a single department), and often span across domains of the hierarchy (providing connections to administrative assistants in other departments, for example). These aunts or administrative assistants are not transmitting anything to one another, but nevertheless still have similar behavioral expectations, revealed from their similar patterns of relationships.12 Drawing on this perspective, we might account for similarities between nodes 2 and 7 in Figure 1.1 as deriving from them being similarly positioned on the periphery of the group.
Table Table 1.1 combines the ideas from above into a set of representative questions commonly found in networks research. This list is by no means comprehensive, but covers a broad sampling from existing research questions. Before we can continue with the central aim of this book to describe methods for capturing the networks that will allow you to examine these types of research questions, we must next address the types of ties that could potentially be measured within any such study.13
|Networks as Cause||Networks as Effect|
|Pipes Metaphor||diffusion of innovations||social integration|
|peer influence||homophilous selection|
|Prisms Metaphor||collective efficacy||vacancy chains|
NOTE: This table is adapted from James Moody with permission.