arXiv subjects

Sofia Maria Nikolakaki

Publications and source records attributed to Sofia Maria Nikolakaki.

3 recordsLinked to original sources

arXiv2021

An Efficient Framework for Balancing Submodularity and Cost

In the classical selection problem, the input consists of a collection of elements and the goal is to pick a subset of elements from the collection such that some objective function $f$ is maximized. This problem has been studied extensively in the data-mining community and it has multiple applications including influence maximization in social networks, team formation and recommender systems. A particularly popular formulation that captures the needs of many such applications is one where the objective function $f$ is a monotone and non-negative submodular function. In these cases, the corresponding computational problem can be solved using a simple greedy $(1-\frac{1}{e})$-approximation algorithm. In this paper, we consider a generalization of the above formulation where the goal is to optimize a function that maximizes the submodular function $f$ minus a linear cost function $c$. This formulation appears as a more natural one, particularly when one needs to strike a balance between the value of the objective function and the cost being paid in order to pick the selected elements. We address variants of this problem both in an offline setting, where the collection is known a priori, as well as in online settings, where the elements of the collection arrive in an online fashion. We demonstrate that by using simple variants of the standard greedy algorithm (used for submodular optimization) we can design algorithms that have provable approximation guarantees, are extremely efficient and work very well in practice.

cs.DS↗

arXiv2020

A Multi-aspect Analysis of Gender Bias on Online Student Evaluations

Institutions widely use student evaluations to assess the faculty's teaching performance, but underlying trends and biases can influence their interpretation. Using data from Rate My Professors, we conduct the largest and most recent quantitative data analysis to study questions related to the evaluation criteria that students have when they review the performance of their male and female professors. Our analysis spans data from two decades (1999-2019), thus taking into account recent changes on the website and in the perception of students, and demonstrates interesting insights related to how students perceive the teaching style and personality traits of their male and female professors. We also present the first analysis that investigates how gender bias evolves over time and changes over space. We believe that our results are interesting from a sociological viewpoint, as they investigate the role of gender in higher education by disclosing how students perceive and evaluate professors of different genders. In addition, we believe that our findings can be useful to educational institutions when considering possible biases that exist in the evaluations of their faculty.

cs.SI↗

arXiv2020

Finding teams that balance expert load and task coverage

The rise of online labor markets (e.g., Freelancer, Guru and Upwork) has ignited a lot of research on team formation, where experts acquiring different skills form teams to complete tasks. The core idea in this line of work has been the strict requirement that the team of experts assigned to complete a given task should contain a superset of the skills required by the task. However, in many applications the required skills are often a wishlist of the entity that posts the task and not all of the skills are absolutely necessary. Thus, in our setting we relax the complete coverage requirement and we allow for tasks to be partially covered by the formed teams, assuming that the quality of task completion is proportional to the fraction of covered skills per task. At the same time, we assume that when multiple tasks need to be performed, the less the load of an expert the better the performance. We combine these two high-level objectives into one and define the BalancedTA problem. We also consider a generalization of this problem where each task consists of required and optional skills. In this setting, our objective is the same under the constraint that all required skills should be covered. From the technical point of view, we show that the BalancedTA problem (and its variant) is NP-hard and design efficient heuristics for solving it in practice. Using real datasets from three online market places, Freelancer, Guru and Upwork we demonstrate the efficiency of our methods and the practical utility of our framework.

cs.AI↗