19 Feb

Sofia Silva: new Master Dissertation on “An experiment about the impact of social influence on the wisdom of the crowds’ effect”

Sofia Silva presented her Master dissertation on the 20th of December 2016, at ISCTE-IUL, entitled “An experiment about the impact of social influence on the wisdom of the crowds’ effect”. The jury was composed by Luis Antunes, Jorge Louçã, and Luis Correia (supervisor).

Groups have the impressive ability to perform better collectively than the best of its individuals. Galton observed this first in 1907 in his ox weight experiment, but the term wisdom of the crowds (WoC) was coined only later in 2004 by Surowiecki. Cognitive diversity at the individual level enables groups to produce differentiated solutions that ultimately cluster near the true value. By cancelling out the wrongs, the aggregation method exposes the convergence of multiple local optima solutions into one, typically an averaged value that comes incredibly close to the truth-value of what is being estimating. Some accounts suggest that social influence hinders the WoC effect because it diminishes the group diversity resulting in biased outcomes. However, social influence is a naturally occurring phenomenon and it is hardly determinable the extent to which individuals are biased or independent given the complexity of the social interactions. We investigated the impact of social influence on the WoC effect by comparing the collective predictions of 4 groups regarding the number of jellybeans in a jar. We demonstrate that the group disclosing full information performs nearly as well as the control group, where no information was shared. The aggregation method to converge the estimates was the arithmetic mean showing that both groups predicted by approximately 7% the correct number. Statistical analysis has shown that diversity is not affected significantly in the social groups. We conclude that the WoC is not affected by social influence but by the degree of aggregation of the social information shared.

21 Mar

Joana Canelas: new master dissertation on Land-Use Intensity and Stability of Ecosystems

Joana Canelas presented her Master Dissertation entitled “Land-Use Intensity and Stability of Ecosystems”, on the 21th of March, 2014. The master dissertation was approved by the jury composed by Tiago Domingos (IST), Henrique Pereira (FCUL, supervisor), and Jorge Louçã (ISCTE-IUL).

Many organisms modify the surrounding environment in order to enhance the availability of resources, although the scale by which human societies do so is unprecedented. Through an ecological network model, we address the relation between ecosystem’s complexity, stability and productivity and how it is affected by land-use intensity, measured as the removal of biomass through harvest. We test different harvest intensities and distributions among species in order to assess the impact of land-use intensity in the ecosystem’s local stability, total biomass remaining and number of species extinctions. We found that land-use intensity triggers a decrease in the frequency of local stable communities. In this regard, our results support the hypothesis that a biomimetic harvest configuration could meet a rising food demand while halting biodiversity loss.

After concluding our Master in Complexity Sciences, Joana got a position of Research Associate at the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig. More recently, she obtained a grant from the University of Kent for developing PhD research on Biodiversity Management, at the School of Anthropology and Conservation (University of Kent).