Data, data, data (from CS50x)

by David J. Malan, Senior Lecturer on Computer Science and Lead Instructor of CS50x 

Version 1 of CS50x debuted on Monday, 15 October 2012, and concluded (unlike my taxes) on Monday, 15 April 2013. We’ve only just begun to dive into all of the data we collected over those six months, but we thought we’d take a moment to share some preliminary datapoints.

Day 0 began roughly as follows:

2:00pm CS50x goes live
2:02pm 500 users online
3:00pm 10,000 users online

Tommy MacWilliam '13, CS50’s, one of CS50’s head TFs, shares even more detail in his blog.

Day n-1, meanwhile, concluded with

150,349 students registered
100,953 students engaged
10,905 pset0 submissions
1,482 project submissions
1,388 certificates awarded

whereby students who “engaged” watched content, asked questions, and used apps, even if they didn’t submit work. Receipt of a certificate required submission of all work with scores of 60% or higher.

Submissions of problem sets and quizzes trended as follows:


Daily engagement in the course, as measured by Google Analytics in terms of unique visitors, trended similarly, peaking early, then reaching some form of equilibrium (that appears to trail off as the course’s end loomed!):

unique visitors

If we zoom in on the course’s final weeks, unique visits hovered around 2,500 per day:

unique visitors

Visits by country, meanwhile, were ordered as follows, with Google Analytics reporting at least one visitor from every country in the world:


As for the students themselves, upon submitting Problem Set 0, students were asked to submit a form that inquired as to their background before CS50x and motivation for taking CS50x. Based on 10,905 submissions (which may or may not be representative of CS50x’s 150,349 registrants), CS50x’s demographics were 20% female and 80% male (whereas CS50 on campus was 36% female in Fall 2012). The average age was 29, with a median of 27 and a mode of 21. CS50x’s eldest student was 80 and youngest student was 10. Even younger were Louis and his brother, who said “hello, world” as well. Though filming those hellos apparently required one take too many.

Per the below, 56% of CS50x students had no prior background in CS, versus 75% in CS50 on campus:

prior courses

Most students had at least a degree from high school, if not beyond:


Out of the 10,905 students who submitted pset0, 10,137 (93%) intended to do all of the course’s work:


To be fair, out of the 150,349 students who registered, only 10,137 (7%) intended to do all of the work (else they’d presumably have submitted at least pset0).

Meanwhile, out of the 10,905 students who submitted pset0, 3,381 (31%) took CS50x because of the prospect of a certificate:

interest in certificates

To be fair, out of the 150,349 students who registered, only 3,381 (2%) took CS50x because of the prospect of a certificate (else they’d presumably have submitted at least pset0).

For most students, then, “success” didn’t necessarily mean a certificate. And “completion” wasn’t necessarily the goal. Among students' motivations for registering were:

Why taking CS50x?

Ultimately, at least 1,388 students will receive a certificate like John Harvard’s here:

John Harvard’s certificate

To put all these numbers into perspective:

  • Among 150,349 students, 100,953 engaged (67%).

  • Among those 100,953 students, 10,905 submitted pset0 (11%).

  • Among those 10,905 students,

    • 3,381 (31%) sought a certificate, and

    • 1,388 (41%) will receive a certificate.

CS50x’s “completion rate” (whereby completion is defined as submission of all work with scores of at least 60%) was thus:

  • 41%, if out of 3,381 who sought a certificate.

  • 13%, if out of 10,905 who submitted pset0.

  • 1.4%, if out of 100,953 who engaged.

  • 0.9%, if out of 150,349 who registered.

By contrast, 703 out of 706 students (99.6%) “completed” CS50 on campus this past fall. But, to be fair, for most CS50x students, “completion” wasn’t necessarily the goal. Indeed, tens of thousands “engaged” in some form.

For the curious, version 2 of CS50x will debut in late 2013 or early 2014 once we’ve had a chance to re-tool and improve! In the meantime, all of version 1’s content will remain freely available at, at, and at as well as in iTunes and iTunes U. And even before version 2 of CS50x debuts, content from Fall 2013 of CS50 itself will become available at in September 2013.