Thread: Need help to prove professor may have altered grades at our university

1. Need help to prove professor may have altered grades at our university

We had a class of 15 students who took an exam: test scores were: 56, 65, 65, 54, 28, 65, 55, 47, 68, 41, 71, 86, 65, 67, 65 respectively on a non multiple choice exam of 50 questions. The passing mark was exactly a 65, so there has been an accusation thrown at our medical school, he decided to bring up the scores. For the people who scored a 65 or above, he wouldnt let them see it, only the people who failed. I know correlation to a statistical test does not determine causation, but I need to find a probability of this happening. Before I accuse someone of something, I want to throw out a statistical significance of an event happening. Anyone know what I can do? Thank you

2. Re: Need help to prove professor may have altered grades at our university

Also if this helps, there was 50 questions, each question being worth 2 points equally.

3. Re: Need help to prove professor may have altered grades at our university

Before I accuse someone of something, I want to throw out a statistical significance of an event happening.
What are you thinking of accusing them of?

4. Re: Need help to prove professor may have altered grades at our university

I want to accuse them of boosting up grades so more people wouldn't fail, the department set a stringent passing mark of 65 so people who were close were given that mark, otherwise they would have to fail more students. However, by university guidelines, this is illegal to do. I need a probability of how 5 people could have attained a score of a 65 on a non mcq test of 50 questions with a class of 15 people. thank you

5. Re: Need help to prove professor may have altered grades at our university

You better hope that there isn't a (Capital "F") Faculty Union that would get involved in this matter.

6. Re: Need help to prove professor may have altered grades at our university

Originally Posted by Dragan
You better hope that there isn't a (Capital "F") Faculty Union that would get involved in this matter.
can i get some help?

7. Re: Need help to prove professor may have altered grades at our university

Originally Posted by swamifez
can i get some help?
as your question stands, i'm pretty sure it's unsolvable. we'd need more information or make widely unrealistic assumptions that will most likely be wrong.

8. Re: Need help to prove professor may have altered grades at our university

How is the scoring done? If I assume 0 points for a wrong answer and 2 points for a correct answer, and no partial points, then no one can get 65 points.

I'm surprised that some students were not allowed to see their work. At our University of Applied Science (in the Netherlands) students are always entitled to feedback on their own work.

I'm no expert in probability but would think of something like what is the probability that 5 or more students out of 15 get the same score.

9. Re: Need help to prove professor may have altered grades at our university

Moderation of results etc? Happens everywhere. Hilarious that you're trying to catch him out though - good luck!

10. Re: Need help to prove professor may have altered grades at our university

Originally Posted by spunky
as your question stands, i'm pretty sure it's unsolvable. we'd need more information or make widely unrealistic assumptions that will most likely be wrong.
Spunky, there could be 3 marks on a question: 0, 1, or 2. There were 50 questions.

There was 18 students:
56, 65, 65, 54, 28, 65, 55, 47, 68, 86, 68, 57, 65, 67, 41, 85, 65, 78

5/18 students actually got a 65 out of 17 students. Probability of that happening?

11. Re: Need help to prove professor may have altered grades at our university

Originally Posted by swamifez
Spunky, there could be 3 marks on a question: 0, 1, or 2. There were 50 questions.

There was 18 students:
56, 65, 65, 54, 28, 65, 55, 47, 68, 86, 68, 57, 65, 67, 41, 85, 65, 78

5/18 students actually got a 65 out of 17 students. Probability of that happening?
I would go for checking the probability on 5 or more students scoring the same grade. You would also be surprised if 6, 7, 8 etc. or more would have the same grade.
This can be seen as a variation on the famous 'birthday problem'. Instead of having 367 possible days, instead of having 2 or more people having the same birthday, we have 5 or more students having the same grade, and we know that the group has 15 people.

The formula for then determining this probability can be found at the bottom of http://math.stackexchange.com/questi...-same-birthday.

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swamifez (10-05-2014)

13. Re: Need help to prove professor may have altered grades at our university

Would you be so vehement or determined if there were 5 100%?

14. Re: Need help to prove professor may have altered grades at our university

Originally Posted by hlsmith
Would you be so vehement or determined if there were 5 100%?
No I wouldn't, but in the history of the English program at our university, there has not been ever one 100%. by him allowing students to go through, he screwed the small minority of students who failed and he knew absolutely what he was doing. i am leaving my university if i can't move onto next year, i spent a lot of money and its an arguement i want to make before i leave.

15. Re: Need help to prove professor may have altered grades at our university

I am trying to figure this out, let X be the number of marks achieved in a single question; then X follows B(2;1/3). Assuming independence, S=X1+⋯X50, the sum of all marks, follows B(100,1/3). Now compute p:=P(S=65). Define Z to be the number of students with S=65. Clearly Z follows B(18,p). Now compute P(Z=5). Would this work?

16. Re: Need help to prove professor may have altered grades at our university

Originally Posted by swamifez
We had a class of 15 students who took an exam: test scores were: 56, 65, 65, 54, 28, 65, 55, 47, 68, 41, 71, 86, 65, 67, 65
You also mentioned somewhere that for each of the 50 questions,
0, 1 or 2 points were awarded. What was the format of questions
and answers? Was it multiple choice? If yes, how did the presentation
of question and answers actually look like, and how was the scoring
performed? Or were these open ended questions, and the rater had to
decide how many points to give to written answers?

With kind regards

K.

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swamifez (10-05-2014)