The Impact of Social Learners on Collective Decision-Making

Post by Lani Cupo

What's the science?

In democratic societies, collective decisions, such as who should hold power, or what action should be taken to address climate change, can drastically impact society. But when people make decisions in groups, the most popular option is sometimes chosen even though it does not have the most merit. This phenomenon is due in part to the presence of those identified here as social learners who adopt the opinions of others instead of critically assessing options for themselves. This week in PNAS, Yang and colleagues developed a mathematical framework for investigating whether there is a critical threshold of social learners that can be present in a collective decision, after which one option may prevail because of popularity, rather than merit. 

How did they do it?

The authors created a dynamical system model which integrated two options (X and Y) with relative merit (m) associated with each option, where m was a number between zero and one. The model incorporated differing proportions of social and independent learners (s) in the population. Finally, it included one parameter as a function that is hypothesized to model two types of conformity, normative (engaging in a behavior because others do it), and informational (engaging in a behavior because it is the right thing to do). The authors derived transition rates between the options for the different types of learners, where social learners will transition between the options based on the popularity of the option, but independent learners transition based on the merit of the option. This allowed the authors to examine the fixed points of the equation, where the proportion of people favoring a given option stops changing. They also investigated how stable these fixed points are when the model is perturbed. Their conclusions remained the same when they changed the model to account for opinion on a spectrum from independent to social, when they only allowed individuals to be impacted only by their local environment, and when they introduced statistical noise to the model. Finally, the researchers simulated a model incorporating the strength of opinion weighting towards option X or Y. 

What did they find?

When X and Y are options with equal merit, there is a critical threshold for the proportion of social learners after which the model bifurcates into two branches, implying either option X or Y could be selected. In the case that the model is not equal between groups, the majority will favor the more meritorious option up to a critical point, but if the proportion of social learners is too high, instability is introduced into the model, meaning there can be cases in collective decision making where the less meritorious option is still chosen. The critical threshold is determined both by the discrepancy in merit between the two options and the conformity function. The threshold that these parameters identify predicts the threshold above which the proportion of social learners harms the decision. Notably, the model is flexible to adapt to different behaviors modelled through the conformity function or to allow parameters, such as the strength of opinions, meaning it represents a flexible tool that can be used to model different situations. 

What's the impact?

This study investigated the impact of social learners on collective decision-making, demonstrating there is a threshold above which social learners may negatively impact the outcome of collective decisions. The outcome of collective decisions can drastically impact daily life—not only in small communities but on a national and global scale as well. The mathematical framework presented provides future studies with the ability to examine social learning in varied and complex scenarios. 

Yan et al. Dynamical system model predicts when social learners impair collective performance. PNAS (2021). Access the original scientific publication here