Update (9/21/21): Added classes up through Spring 2021, updated from Fall 2019.

Where is this data from?
All data comes from SCU Course Evaluations. These are the online surveys filled out by students at the end of each quarter. This data includes over 27,000 surveys from Spring 2015 through Spring 2021. This excludes classes from Winter, Spring, and Summer 2020, as SCU did not put out evaluations for this period.
How do you determine the "quality" value?
The SCU Course Evaluation survey asks various questions about the quality of an instructor's teaching. This value is the average of all of those questions. This value is reported under Overall Indicators > 1. Items 1.1-1.9 > av. on the first page of the course evaluation PDF.
How do you determine the "difficulty" value?
On the SCU Course Evaluation survey, question 2.2 asks "[How] conceptually challenging [was this course] compared to most courses I have taken at SCU?" The average value for the class is available on the PDF. This is the difficulty value of a class.
How do you determine the "weekly workload" value?
The SCU Course Evaluation survey asks "In an average week, the approximate number of hours I spent doing work for this course outside regularly scheduled class/lab time was?" The weighted sum of the hours and percentages yields the weekly workload value.
Where can I learn more?
I wrote up a piece about this website on my blog. Feel free to check it out to get the story behind this website!