My own experience
I remember during our second year in engineering when we took social science courses (GSP 201, GSP 202, etc). A lot of us in engineering admitted that social science courses are really hard. To me, it was quite stressful trying to memorize a lot of definitions from different schools of thought, arguments, counter-argument, dates, etc. Most students in engineering find calculation easier to deal with than "theory" (as we refer to courses like GSP). But then some students from Biochemistry who "borrowed" one of our courses described the course as "hell." Meaning they found the engineering course difficult to grasp. A couple of times I also met some students from FST (Food Science Technology) in our mechanical engineering laboratory. They didn't find it funny either. So the bottom line before we start looking at courses which have been rated hardest is what I have said earlier: no course should be regarded as easy because people differ in what they find easy or difficult. Any course can be hard or easy depending on whom you bring it to. However, another fact worth mentioning is that over time statistics have shown that some courses might be really harder than others. Not only that those courses require more amount of time and effort, but they are also more challenging that a significant number of students quit along the way.
Rating sources
The ratings in this post are based on ratings from different sources which I put together to get a clearer pattern. Some sources rated the courses based on dropout rates (an example is a rating by telegraph.co.uk), some by individual courses (like this one by listsurge.com), and some based on the field of study (example The 10 Hardest College Degrees by outstandingcolleges.com). Where subjects are used for the rating I try to find the courses that are related to the subjects. For example, engineering is basically the application of physics and mathematics. So, if physics and math are rated very hard, engineering is likely very hard as well. All the ratings may not agree but in the end, we find that some courses are always near the top and some near bottom of the ratings.Hardest courses/degrees
Note: The rating is in ascending order. In other words, the course at the bottom (that is number 1) is rated hardest while the course at the top (that is number 10) is rated easiest.
10) Education
9) Arts & Humanities
8) Philosophy and Religion
7) Social/Behavioral Sciences: sociology, psychology, anthropology, etc.
6) Physical Sciences: geology, physics, chemistry, mathematics, etc.
5) Business & Management
4) Biological sciences: Biochemistry, Microbiology, etc.
3) Architecture
2) Medical Sciences: medicine, pharmacy, veterinary medicine, anatomy, etc.
1) Engineering: aeronautics, mechanical engineering, electrical engineering, etc.
So, based on the ratings, engineering courses are the hardest to study!
