Standard Deviations and Tests?

[D0CTORX]

So can someone explain to me how that works? My professor didn't explain it.

So the average for test 1 was 88, and I was below, I had a 84, and the standard deviation was a 12.85. Does that mean I have like a C-? or what for that test?

The next test average was 70, I scored a 88, and standard deviation was a 17. Does that mean I did well?

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[woltej1]

a standard deviation means that a little less than 70% of the scores were plus or minus that standard deviation from the mean. A small standard deviation means that the scores were fairly close while a large means they differed by a lot..

 

[pietachok]

So can someone explain to me how that works? My professor didn't explain it.

So the average for test 1 was 88, and I was below, I had a 84, and the standard deviation was a 12.85. Does that mean I have like a C-? or what for that test?

The next test average was 70, I scored a 88, and standard deviation was a 17. Does that mean I did well?

If the average is set at the cutoff point between C+ and B-, then typically each increase/decrease in score by 1/3 of a standard deviation above/below the mean will represent the cutoff to the next grade. In other words, scores within 1/3 standard deviation above the mean will get a B-, 1/3 to 2/3 of a standard deviation above the mean get a B, then 2/3 to 1 standard deviation above get a B+ . . . by this scoring, you would get a C+ on the first exam and an A- on the second exam.

That said, not all professors use this standard when grading on a curve.