August 2nd, 2017, 09:08 PM  #11 
Global Moderator Joined: Dec 2006 Posts: 20,098 Thanks: 1905 
There's too little data for complicated mathematics to be worthwhile. The nature of the quiz (untimed, open book, etc.) suggests that a student should have to do really well to get an A. From what you stated, I would guess that the number of points attained reflected not so much the ability of each student, but mainly the amount of careful thought that was applied in reading and answering the questions. I chose grade bands of equal "width", making that width quite generous. Showing the results (for this particular quiz) on a histogram suggests that the width shouldn't be larger. Being any more generous would allow students to "pass" even if they've answered most of the questions incorrectly. The grade width could be smaller, but that would split up the students who score 1821 points, which could attract criticism unless you feel strongly that it's right to do so. As it is, more than 75% of your students "passed". If you made the grades tougher, the significant effect would probably be that 1417 points would no longer be considered satisfactory. Letter grades are not intended to be converted back to points. 
August 3rd, 2017, 05:02 AM  #12 
Senior Member Joined: Jun 2014 From: USA Posts: 438 Thanks: 30 
Thank you everyone

August 3rd, 2017, 06:13 AM  #13  
Senior Member Joined: May 2016 From: USA Posts: 1,250 Thanks: 516  Quote:
Decide where you want failure to be and fail those below that bright line. Decide where you want an A to be, and give an A to all those above that bright line. Decide the number of gradations you want for the remainder, for example B, C, and D would be 3, calculate the reciprocal (1/3rd in my example) and assign the top 1/3rd a B, the middle 1/3rd a C, and the bottom 1/3rd a D. Grading on a curve is an exemption, not a science.  

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