Person: Malan, David
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Malan, David
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Publication Going Over the Cliff: MOOC Dropout Behavior at Chapter Transition(Informa UK Limited, 2020-01-02) Chen, Chen; Sonnert, Gerhard; Sadler, Philip; Sasselov, Dimitar; Fredericks, Colin; Malan, DavidParticipants’ engagement in massive online open courses (MOOCs) is highly irregular and self-directed. It is well known in the field of television media that substantial parts of the audience tend to drop out at major episodic, or seasonal, closures, which makes creating cliff-hangers a crucial strategy to retain viewers (Bakker, 1993; Cazani, 2016; Thompson, 2003). Could there be an analogous pattern in MOOCs—with an elevated probability of dropout at major chapter transitions? Applying disjoint survival analysis on a sample of 12,913 students in a popular astronomy MOOC that built participants’ cultural capital (hobbyist pursuits), we found a significant increase in dropout rates at chapter closures. Moreover, the latter the chapter closure was positioned in the course sequence, the higher the dropout rate became. We found this pattern replicated in a sample of 20,134 students in a popular computer science MOOC that introduced participants to programming.Publication Scaling Office Hours: Managing Live Q&A in Large Courses(2012) Macwilliam, Thomas; Malan, DavidComputer Science 50 (CS50) is Harvard University’s introductory course for majors and nonmajors alike. So that students have an adequate support structure with which to tackle the course’s weekly programming assignments, we offer weekly “office hours,” during which students can receive one-on-one help from teaching assistants. In Fall 2010 and years prior, office hours were held in a basement-level computer lab. However, this environment did not appeal to staff or students. Moreover, this format for office hours suffered from logistical inefficiencies, repetition of questions among students, and lack of communication among staff, which led to high wait times for students. We relocated office hours in Fall 2011 to dining halls to create a more social and collaborative workspace, with more staff on duty at once. We also developed CS50 Queue, a web- and iPadbased system for managing office hours’ logistics. Overall, the new format proved a success. Attendance at office hours grew more than linearly, with an average of 120 students attending per night, up from 30 students in 2010 despite only a 23% increase in enrollment. Even though Queue enabled us to scale, new logistical challenges arose, and wait times for students still sometimes exceeded an hour. We intend to address those challenges in Fall 2012 in order to reduce wait times to 15 minutes at most.Publication CS50 Sandbox: Secure Execution of Untrusted Code(Association for Computing Machinery, 2013) Malan, DavidWe introduce CS50 Sandbox, an environment for secure execution of untrusted code. Implemented as an asynchronous HTTP server, CS50 Sandbox offers clients the ability to execute programs (both interactive and non-interactive) written in any compiled or interpreted language in a tightly controlled, resource-constrained environment. CS50 Sandbox’s HTTP-based API takes files, command lines, and standard input as inputs and returns standard output and error plus exit codes as outputs. Atop CS50 Sandbox, we have built CS50 Run, a web- based code editor that enables students to write code in a browser in any language, whether compiled or interpreted, that’s executed server-side within a sandboxed environment. And we have built CS50 Check, an autograding framework that supports black- and white-box testing of students’ code, leveraging CS50 Sandbox to run series of checks against students’ programs, no matter the language of implementation. We present in this work the pedagogical motivations for each of these tools, along with the underlying designs thereof. Each is available as open source.Publication From Cluster to Cloud to Appliance(Association for Computing Machinery, 2013) Malan, DavidWe propose a client-side virtual machine (VM) as an alternative to on-campus clusters and off-campus clouds as a development environment for students in introductory courses. In Fall 2011, we deployed the CS50 Appliance, our own such VM, to 600 students on campus and, in Fall 2012, to 700 students on campus and 140,000 students online. We present in this work the results of that two-year experiment. The appliance itself is available as open source for others to adapt or adopt. Not only did the appliance enable us to provide students with simpler tools, among them a graphical editor without any latency, it also enabled us to provide more sophisticated tools too, including a web server and database server. Moreover, the appliance ensured that the course's workload no longer required constant Internet access, particularly of students abroad. And the appliance alleviated load on the course's servers, with execution of students' programs now distributed across students' own CPUs. Without the appliance (or more costly clusters or clouds), we certainly could not have accommodated as many as 140,000 students. But some students' laptops, particularly netbooks, struggled under the appliance's weight. Even though designed to be lean, the appliance, like any VM, still consumes resources, particularly RAM. And unforeseen technical difficulties arose in both years, most, but not all, of which we redressed with mid-semester updates and documentation. Overall we have judged our deployment of an appliance a success, superior to past years' clusters and clouds. And we continue to refine the appliance for Fall 2013.Publication Engaging Students through Video: Integrating Assessment and Instrumentation(Association for Computing Machinery, 2013) Macwilliam, Thomas; Aquino, R.J.; Malan, DavidCS50 is Harvard’s introductory course for majors and non-majors alike. For years, we have posted videos of the course’s lectures and sections online for the sake of review and distance education alike. But students’ experience with these videos has been historically passive. Students have been able to watch the course’s content on demand, rewinding and fast-forwarding at will, but they have not had means to engage interactively with the content or to check their understanding of material while watching videos. Furthermore, while we collected basic usage data (e.g., how many times a video was viewed), we lacked detailed analytics describing, for example, which portions of a video were commonly skipped or watched multiple times by students. To make videos more immersive and engaging for students, we developed CS50 Video, an open-source video player for desktop and mobile devices. CS50 Video allows instructors to integrate assessment questions to be answered by students at their own pace or at specific points in time directly into a video player. CS50 Video also allows students to search over video transcripts to find content easily as well as view videos at variable playback speeds (in order to make videos more accessible for ESL learners). Finally, CS50 Video integrates with third-party analytics solutions to allow instructors to view detailed usage statistics describing how students are interacting with videos (e.g., which videos or portions of videos are commonly watched or skipped over). We have deployed CS50 Video to students taking CS50 online and have obtained preliminary results. Because CS50 Video stores responses to questions server-side, we have been able to track students’ performance on in-video assessments. Thus far, we have observed that only 28% of students who watch online videos have engaged with assessment questions. Students who answer an assessment question incorrectly on their first attempt will often try again until reaching a correct answer, with 84.5% of correct answers reached in at most three attempts. We next plan to analyze the effects of in-video assessments on students’ mastery of material and introduce A/B-testing functionality for questions. We also plan to use students’ performance on assessments to understand the topics with which students struggle.Publication Streamlining Grading toward Better Feedback(Association for Computing Machinery, 2013) Macwilliam, Thomas; Malan, DavidCS50 is Harvard University's introductory course aimed at majors and non-majors alike. Each week, students complete programming assignments and have traditionally received feedback from staff in the form of comments on PDFs of their code. Staff have historically reported spending significant amounts of time grading because of bottlenecks that included generating PDF documents and manually emailing feedback to students. Because we preferred that staff spend less of their time on grading logistics and more time providing feedback and helping students online or in person, we set out to improve the efficiency of the grading process. In Fall 2012, we developed and deployed CS50 Submit, a web-based utility through which staff can leave feedback for students via inline "sticky notes." Following the introduction of CS50 Submit, staff reported grading for 10% fewer hours (i.e., 42 minutes) per week and 13% fewer minutes (i.e., 4 minutes) per student, even while providing as much or more feedback. Meanwhile, we observed significantly higher levels of engagement with the course's online discussion board among staff, suggesting a more favorable distribution of staff workload. With CS50 Submit, we have also been able to audit exactly how much time staff spent grading each week in order to identify additional bottlenecks. Using CS50 Submit, we also observed that, on average, 9% of students each week never read their graders' comments, with a peak one week of 14%. The number of students who did not read feedback increased with time, which has led us to question whether asynchronous, textual comments are the most effective feedback mechanisms for students. In future terms, we plan to experiment with in-person, interactive means of delivering feedback to students. In this paper, we present CS50 Submit and the insights it has yielded into the behavior of students and staff alike.Publication Moving CS50 into the Cloud(2010) Malan, DavidIn Fall 2008, we moved Harvard College’s introductory computer science course, CS50, into the cloud. Rather than continue to rely on our own instructional computing infrastructure on campus, we created a load-balanced cluster of virtual machines (VMs) for our 330 students within Amazon Elastic Compute Cloud (EC2). Our goals were both technical and pedagogical. As computer scientists, we wanted more control over our course’s infrastructure (e.g., root access), so that we ourselves could install software at will and respond to students’ needs at any hour without an IT department between us and our systems. As teachers, we wanted easier access to our students’ work (as via su) as well as the ability to grow and shrink our infrastructure as problem sets’ computational requirements demanded. But we also wanted to integrate into the course’s own syllabus discussion of scalability, virtualization, multi-core processing, and cloud computing itself. What better way to teach topics like those than to have students actually experience them. Although Amazon supported our experiment financially with credits, it was not without costs. Serving as our own system administers cost us time, as did some self-induced late-night technical difficulties. But the upsides proved worth it, as we accomplished our goals. We present in this paper what we did right, what we did wrong, and how we did both so that others can more easily build their own home in the cloud.Publication Reinventing CS50(Association for Computing Machinery, 2010) Malan, DavidComputer Science 50 is Harvard College’s introductory course for majors and non-majors alike, enrollment in which both rose and fell along with the dotcoms. Although enrollment peaked in 1996 at 386 students, it had settled by 2002 in the neighborhood of 100. We set out in 2007 to combat that trend by tackling two problems. We hypothesized that CS50 suffered from two, one of perception and one of design. Although, per end-of-term surveys, the course had never lacked for good teachers or good content, the consensus on campus for years had been to beware this particular course. And the course’s own syllabus may very well have been dated in the eyes of students who had begun to carry regularly modern hardware and software in their backpacks and pockets. Not only did we proceed to revamp every one of CS50’s problem sets, we brought its syllabus more in line with technological trends already familiar to students. And we altered the tone of the course to appeal to those “less comfortable” with computing on campus. But we took care to preserve the course’s rigor and underlying fundamentals, lest we do our own students a disservice. Our new approach appears to be working. Between 2006 and 2007, enrollment in CS50 more than doubled from 132 to 282 (+114%). Between 2007 and 2008, enrollment increased another 17% to 330, though even more striking was that year’s 48% increase in female enrollment. By 2009, enrollment remained strong at 338. We present in this work what we have done and why we have done it.Publication Advanced Forensic Format: An Open, Extensible Format for Disk Imaging(International Federation for Information Processing, 2006) Garfinkel, Simson; Malan, David; Dubec, Karl-Alexander; Stevens, Christopher; Pham, CecileThis paper describes the Advanced Forensic Format (AFF), which is designed as an alternative to current proprietary disk image formats. AFF offers two significant benefits. First, it is more flexible because it allows extensive metadata to be stored with images. Second, AFF images consume less disk space than images in other formats (e.g., EnCase images). This paper also describes the Advanced Disk Imager (AImage),a new program for acquiring disk images that compares favorably with existing alternatives.Publication Podcasting Computer Science E-1(Association of Computing Machinery, 2007) Malan, DavidIn recent months [teachers have] become publishers of content and students subscribers thereof by way of podcasts, feeds of audio, video, and other content that can be downloaded to clients like iTunes and devices like iPods. In the fall of 2005, we ourselves began to podcast Harvard Extension School's Computer Science E-1 in both audio and video formats, the first course within Harvard University to do so. Our goals were to provide students with more portable access to educational content and to involve them in technology itself.To evaluate this experiment, we have analyzed logs and surveys of students. We find that our students valued E-1's podcast more as a vehicle for review (45%) than as an alternative to attendance (18%). We also find that most students (71%) tended to listen to or watch lectures on their computers, with far fewer relying upon audio-only (19%) or video (10%) iPods. We argue, meanwhile, that podcasting, despite its widespread popularity, is but a marginal improvement on trends long in progress. It is this technology's reach that we claim is significant, not the technology itself. Logs suggest that E-1's own podcast, available not only to students but to the public at large, has acquired (as of September 2006) between 6,000 and 10,000 subscribers from over 50 countries. We argue, then, that podcasting offers to extend universities' educational reach more than it offers to improve education itself.