*3.2. Measures*

Participants were asked to fill in a questionnaire at four time points: after the first in-group meeting (Time 1—planning the strategy, before interacting with the other groups), and after each of the three plenaries (Times 2, 3, and 4)—the round table meetings where delegates attempted to integrate the information they had collected during visiting times and to reach consensus. The questionnaire was based on a round robin procedure (each stakeholder evaluated all the other stakeholders in the system including self-ratings) and included measures of trust and collaborative relations. The questionnaire at Time 1 evaluated the expectations one had regarding the trustworthiness and collaboration of the stakeholders in the system, and at Times 2, 3, and 4, the items referred to perceptions regarding the experienced collaborativeness of each stakeholder.

At Time 1 we used a round robin procedure to evaluate the expected trustworthiness of one's own and the other groups, on a seven-point Likert scale (1 = "not at all" to 7 = "very much"). The item was worded as follows: *Based on the information you have gathered so far, how trustworthy is the organization "X"*? Trust self-enhancement was evaluated using a procedure described in Kwan et al. (2004) as the difference between self-rated trust and trust ascribed to all the other stakeholders in the system. According to Kwan et al. (2004), this self-enhancement index reflects (favorable) social comparison processes or the extent to which the members of a stakeholder group perceive their own group as more trustworthy than they perceive the other stakeholders in the system.

To compute network centrality, we used a matrix approach, and asked respondents to generate pairwise evaluations of the collaboration between the stakeholders in the system: *Based on the information you have gathered so far, please rate the quality of the relation between all the organizations*. Therefore, we asked participants to fill out a matrix containing all dyadic relations among stakeholders. The evaluations were made on a scale between −5 and +5 (where −5 refers to a very conflictual relation and +5 to a very collaborative relation, 0 represents the absence of conflict or the absence of collaboration). Therefore, to estimate the collaborative ties, we have recoded all negative values as zero. We have focused on the ties participants reported for their own group as these are most likely to be the accurate representations of the collaborative relations in MPSs (participants might have had misconceptions about the relations among other groups in the MPS) (Casciaro 1998). As such, the centrality indices were computed by aggregating individual perceptions of own group centrality in the context of the MPS network. Networks were generated for each group, in each session, at four time intervals. As indicators of network centrality, we have used two indices that estimate centrality for each stakeholder in the network relative to the rest of the network, namely closeness and betweenness centrality. Closeness centrality is a measure defined as the sum of geodesic distances from a node to all others in the network. Geodesic distance from a node to another node is the length of the shortest path connecting them (Freeman 1979). In other words, closeness centrality is an estimate of how central a particular stakeholder in the generic MPS network is. A stakeholder with high closeness centrality indicates that the members of the respective stakeholder group perceive it "in the middle" of the MPS network. Betweenness centrality is a measure of how often a given node falls along the shortest path between two other nodes, and is typically interpreted in terms of the potential for controlling flows through the network. The betweenness of a target stakeholder in the MPS network estimates the relative number of stakeholder pairs that can only communicate with each other via the target stakeholder. Therefore, a node with a high betweenness is very likely to have substantial power because it can control the possibility of other nodes reaching each other via efficient paths (Freeman 1979).
