Editing Small-world experiment (section)

==The Reversal Small-World Experiment==
The Reversal Small-World Experiment is a 1978 study conducted by Peter D. Killworth and H. Russell Bernard, aiming to test and refine the understanding of the small-world phenomenon. This phenomenon suggests that individuals in a social network are connected by surprisingly short chains of acquaintances. The study builds upon the pioneering work of Stanley Milgram. Killworth and Bernard introduced a reversal approach to the experiment, addressing key limitations in Milgram’s methodology and testing the validity of his conclusions regarding the structure and reachability of social networks. 

===Motivation===
Milgram’s original experiment relied on forward routing, where participants were tasked with passing messages to a target person by selecting acquaintances they believed were closest to the destination. However, Milgram’s findings were limited by:
#High attrition rates: Many message chains never reached their destination, leading to incomplete data.
#Cognitive biases: Participants might not have accurately assessed who among their acquaintances was closest to the target.
#Structural biases: The small-world model assumes a connected network, but real-world networks contain isolated subgroups.
To address these issues, Killworth and Bernard designed an experiment where messages started from the target person and traced paths backward through networks to the originating participants. This reversal method aimed to provide a more accurate measure of social reachability and improve the understanding of network structures.

===Methodology===

====Experimental Design====
Killworth and Bernard conducted their study using two separate experimental setups:
#Forward Small-World Task – Similar to Milgram’s method, participants attempted to send a message to a known target by passing it through their acquaintances.
#Reversal Small-World Task – Instead of moving forward, the target person initiated the process by attempting to trace how messages would have traveled in reverse through the social network.

====Data Collection====
The study involved diverse groups of participants from different social settings, aiming to compare various types of social networks. The researchers asked participants: to estimate how many intermediaries would be needed to connect them to a randomly chosen person, to list and categorize their acquaintances, including professional, familial, and casual relationships and to assess how well they could predict social distances.
The key differences from Milgram’s experiment were: the reverse tracking of connections rather than relying on participants' ability to forward messages. An emphasis on estimating social ties, rather than simply measuring completion rates of message chains. An analysis of clustering patterns, determining whether certain groups (e.g., work colleagues vs. family) were more effective in forming short chains.

====Results and Findings====
#Overestimation of Social Distances: Participants in the experiment overestimated the number of intermediaries needed to connect to a random person. While Milgram’s study suggested an average of six degrees of separation, Killworth and Bernard found that people often believed longer chains were necessary. This suggests that humans have difficulty perceiving their true connectivity within a social network.
#Higher Completion Rates in Reverse Networks: The reversal method produced higher completion rates compared to Milgram’s forward method. This suggested that targets were better at identifying people who could link them to participants than participants were at identifying paths forward and social networks are structured in a way where certain central individuals (hubs) play a crucial role in connectivity.
#Network Clustering and Social Categories: Killworth and Bernard found that people tend to cluster into distinct social categories, such as: family networks, workplace/professional networks, friendship networks and community/religious groups. Interestingly, different networks exhibited varying levels of efficiency in message passing. Professional networks tended to be more interconnected, while family networks were more closed but highly efficient within small groups.
#Limitations of Milgram’s Forward Routing: One of the most significant findings was that Milgram’s experiment might have underestimated the number of connections needed to reach a target. Since many messages in Milgram’s study never reached their destination, his estimate of “six degrees of separation” may have been biased. Killworth and Bernard’s reverse approach suggested that actual connectivity varied widely based on network structure.
#Role of “Hubs” in Social Connectivity: The reversal experiment highlighted that certain individuals act as highly connected nodes, or hubs, in social networks. These individuals often play a disproportionate role in connecting distant groups, reinforcing the idea that social networks are not random but structured around a few key connectors.<ref>{{cite thesis |last1=Killworth |first1=Peter D. |author-link1=Peter Killworth |last2=Bernard |first2=H. Russell |date=1978 |title=The Reversal Small-World Experiment |url=http://snap.stanford.edu/class/cs224w-readings/killworth78smallworld.pdf |location= |publisher=Elsevier Sequoia S.A., Lausanne |access-date=25 March 2025}}</ref>