Sergiy O Nesterko

Due dates in MOOCs: does stricter mean better?

Massive Open Online Courses (MOOCs) employ a variety of components to engage students in learning (eg. videos, forums, quizzes). Some components are graded, which means that they play a key role in a students final grade and certificate attainment. It is not yet clear how the due date structure of graded components affects student outcomes including academic performance and alternative modes of learning of students. Using data from HarvardX and MITx, Harvards and MITs divisions for online learning, we study the structure of due dates on graded components for 10 completed MOOCs. We find that stricter due dates are associated with higher certificate attainment rates but fewer students who join late being able to earn a certificate. Our findings motivate further studies of how the use of graded components and deadlines affects academic and alternative learning of MOOC students, and can help inform the design of online courses.

Bias–Variance and Breadth–Depth Tradeoffs in Respondent-Driven Sampling

Respondent-driven sampling (RDS) is a link-tracing network sampling strategy for collecting data from hard-to-reach populations, such as injection drug users or individuals at high risk of being infected with HIV. The mechanism is to find initial participants (seeds), and give each of them a fixed number of coupons allowing them to recruit people they know from the population of interest, with a mutual financial incentive. The new participants are again given coupons and the process repeats. Currently, the standard RDS estimator used in practice is known as the Volz–Heckathorn (VH) estimator. It relies on strong assumptions about the underlying social network and the RDS process. Via simulation, we study the relative performance of the plain mean and VH estimators when assumptions of the latter are not satisfied, under different network types (including homophily and rich-get-richer networks), participant referral patterns, and varying number of coupons. The analysis demonstrates that the plain mean outperforms the VH estimator in many but not all of the simulated settings, including homophily networks. Also, we highlight the implications of multiple recruitment and varying referral patterns on the depth of RDS process. We develop interactive visualizations of the findings and RDS process to further build insight into the various factors contributing to the performance of current RDS estimation techniques.