# Assuming professors' curves are not auto-spikers but normalizers, what's the average distribution?

**URL:** <https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928>\
**Category:** Factual Questions\
**Created:** [April 19, 2011, 3:42am UTC](https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928 "2011-04-19T03:42:15Z")\
**Posts on this page:** 8\
**Page:** 2

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**Author:** ![Farmer\_Jane](https://avatars.discourse-cdn.com/v4/letter/f/bbe5ce/32.png) [@Farmer\_Jane](https://boards.straightdope.com/u/Farmer_Jane)\
**Post date:** [April 19, 2011, 10:50pm UTC](https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928/21 "2011-04-19T22:50:57Z")

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> [@Chronos](#):
>
> You also can’t say, a priori, how many students “should” get As, or how many should get Bs, or whatever. To do that, you’d have to already know what distribution you wanted for grades. And the way such distributions are usually established in the first place is by some teacher or department head deciding how many students should get As, and so on.
> 
> Also be aware that the 90-80-70-60 grading scheme is far from universal, especially once you get to college. There’s a good argument to be made that a well-designed test will have an average of 50%, and I’ve had classes where the top grade (which got an A) was 25 or 30%.

First paragraph: That’s what’s wrong with education.

Second paragraph: True. But you should always test more than once. It not only makes you a better teacher, but it’s science. Unfortunately, serious college programs are more about competition than teaching.

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**Author:** ![Farmer\_Jane](https://avatars.discourse-cdn.com/v4/letter/f/bbe5ce/32.png) [@Farmer\_Jane](https://boards.straightdope.com/u/Farmer_Jane)\
**Post date:** [April 19, 2011, 10:52pm UTC](https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928/22 "2011-04-19T22:52:41Z")

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> [@billfish678](#):
>
> Uhhh, I think thats kinda what I was complaining about…

You quoted a sentence and then called it two sentences and I misread your intent. 😃 Sorry!

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**Author:** ![miragesyzygy](https://avatars.discourse-cdn.com/v4/letter/m/46a35a/32.png) [@miragesyzygy](https://boards.straightdope.com/u/miragesyzygy)\
**Post date:** [April 20, 2011, 3:59am UTC](https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928/23 "2011-04-20T03:59:12Z")

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> [@](#):
>
> What Gladwell is saying that anyone with an I.Q. above 105 is intelligent enough to succeed at college. He is not saying that the average I.Q. of people who are intelligent enough to succeed at college is 105.

105 at the minimum rather than at the 50% mark makes more sense. Gladwell didn’t specify though, but a 105 average would indeed make an nearly useless qualification on the population.

> [@](#):
>
> And that’s about the end of what we can say. Without detailed knowledge of the IQ distribution of the college students we’re out of data.

Is there a strong enough correlation between IQ and SAT scores to base observations off the latter?

> [@](#):
>
> “\>90% correct = A, \>80% = B, \>70% = C, \>60% = D, else F” there is still the meta-normalization that somebody had to decide how hard to make the test. And that decision controls the grade distribution outcome at least as much as the students’ efforts do.

But students, coming into the test room with different aptitudes, might perform to levels correlational to their aptitudes.

> [@](#):
>
> You also can’t say, a priori, how many students “should” get As, or how many should get Bs, or whatever. To do that, you’d have to already know what distribution you wanted for grades. And the way such distributions are usually established in the first place is by some teacher or department head deciding how many students should get As, and so on.

But if the grading assignment is not discretionarily decreed, (otherwise, a policy to allow for 30% of the student to receive A’s would leave us with just that), but rather fixed, and neglecting the concrete number at which an A is floored (i.e., not debating about whether an A is a 90 or a 93), is it easier to answer “what percentage of students can get X% of the total possible points?” Or at least, how might the question be phrased to allow a fair if inexact answer?

> [@](#):
>
> As an addendum to this post, (a) what percent of students make the “Dean’s List”, or “honours”, or “cum laude” or whatever they call the top performers at your institute of choice, and (b) what was the cut-off criteria?

Some colleges set _summa cum laude_ at 5% of the graduating class, but are the 5% who receive it the same as the people who are capable of receiving it?

> [@](#):
>
> It’s a nice story, but I’m telling you what I and others have seen in actual classes at elite universities, where you can be comfortable that the average IQ is above 105.

Gladwell spoke of colleges in general, but how redshifted would an elite college’s students’ be?

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**Author:** ![Wendell\_Wagner](https://avatars.discourse-cdn.com/v4/letter/w/8491ac/32.png) [@Wendell\_Wagner](https://boards.straightdope.com/u/Wendell_Wagner)\
**Post date:** [April 20, 2011, 7:14am UTC](https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928/24 "2011-04-20T07:14:57Z")

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miragesyzygy writes:

\> 105 at the minimum rather than at the 50% mark makes more sense. Gladwell  
\> didn’t specify though, but a 105 average would indeed make an nearly useless  
\> qualification on the population.

Not really. About 37% of the population have an I.Q. of 105 or greater. Gladwell is saying then that a little more than a third of the population are capable of graduating from college, if you based their ability purely on I.Q. That’s not terribly different from the proportion of people who do spend some time at college in the U.S.

\> Gladwell spoke of colleges in general, but how redshifted would an elite  
\> college’s students’ be?

I don’t know really, but I suspect that the equivalent for an elite college might be about 130. 2% of the population have an I.Q. of 130 or above, so that would be around one in fifty. Please note carefully what’s being said here. The claim is not that 105 is the average I.Q. of the people who can succeed at an ordinary college. The (probably equivalent) claim is not that 130 is the average I.Q. of those who can succeed at an elite college. The claim is that if everybody with an I.Q. of 105 or above went to college and worked hard, they could all graduate (but the ones with I.Q.'s of around 105 would indeed have to work very hard). The equivalent claim (I suspect) is that if everybody with an I.Q. of 130 or above went to an elite college and worked hard, they could all graduate (but those with I.Q.'s of around 130 would indeed have to work very hard).

Also, please let me repeat what I said in my first post. To make the statements above, we need to pretend for a second that I.Q. is actually an accurate measure of something that we’ll call intelligence. We also need to pretend for a second that intelligence is the only thing that would determine one’s ability to succeed in college. I consider each of those statements to be shaky, but I have no intention of arguing about them. I’m only assuming them so that I can answer your questions based purely on the numbers.

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**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\
**Post date:** [April 20, 2011, 3:04pm UTC](https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928/25 "2011-04-20T15:04:16Z")

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> [@md2000](#):
>
> Of course, if the lowest IQ you can hope to make it through on is 105, then odds are a lot of 105-115 will choose alternate paths to success. Then, elite colleges tend to admit based on test scores that will weed out a lot of the lower end of the acceptable range whose father was not a big-shot alumni. This may or may not be balanced out by those who are more than qualified scholastically but not financially for ivy league. Regardless, the bottom lobe will be truncated. For every high-grade genius in third-year math, one hopes there is not a special needs student to balance the distribution.

> [@ultrafilter](#):
>
> I have no idea what you’re trying to say here.

In \<105 terms:

There will be plenty of smart college attendees producing a significant higher-IQ side of the distribution graph of students. But with a few notable exceptions, there should be almost nobody in the lower side of the graph. So the IQ distribution graph will not be symmetrical. It will be chopped off at the lower end, jump to a high number then slowlytaper off at the high end. If we assume IQ means something and marks follow IQ, then the marks distribution in classes will also show this asymmetry - almost nobody below D, but a decent number in B and less but still quite a few with A, fewer with A+. Almost like a bell curve, but with lowest portion cut off.

Theoretically, then, marks will NOT follow a bell curve (a normal distribution).

I was looking for an example/name of this (it’s been a long time since I did real math) What comes to mind is the Pareto curve. I suspect the curve will be more pronounced in the more prestigious universities. The best I could find was - i imagine a curve shaped like this:  
this [http://www.google.ca/imgres?imgurl=http://www.blazelabs.com/pics/plancktondist2.gif&imgrefurl=http://www.blazelabs.com/f-g-relmass.asp&usg=\_\_dWME3bWuJRNMZ\_2z8D8hIh2M14E=&h=350&w=441&sz=17&hl=en&start=5&zoom=1&tbnid=vBrsCbS\_jJBpPM:&tbnh=101&tbnw=127&ei=KvWuTe3sI8rx0gGj1qG6Cw&prev=/search%3Fq%3Ddistribution%2Bcurve%26hl%3Den%26sa%3DG%26biw%3D1050%26bih%3D661%26gbv%3D2%26tbm%3Disch&itbs=1](http://www.google.ca/imgres?imgurl=http://www.blazelabs.com/pics/plancktondist2.gif&imgrefurl=http://www.blazelabs.com/f-g-relmass.asp&usg=__dWME3bWuJRNMZ_2z8D8hIh2M14E=&h=350&w=441&sz=17&hl=en&start=5&zoom=1&tbnid=vBrsCbS_jJBpPM:&tbnh=101&tbnw=127&ei=KvWuTe3sI8rx0gGj1qG6Cw&prev=/search%3Fq%3Ddistribution%2Bcurve%26hl%3Den%26sa%3DG%26biw%3D1050%26bih%3D661%26gbv%3D2%26tbm%3Disch&itbs=1)

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**Author:** ![ultrafilter](https://avatars.discourse-cdn.com/v4/letter/u/3d9bf3/32.png) [@ultrafilter](https://boards.straightdope.com/u/ultrafilter)\
**Post date:** [April 20, 2011, 5:01pm UTC](https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928/26 "2011-04-20T17:01:02Z")

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> [@md2000](#):
>
> Theoretically, then, marks will NOT follow a bell curve (a normal distribution).

Again, this does not jibe with my experience as a teaching assistant at an elite university, nor with anyone else’s. I’ve already explained why we would expect to see normally distributed scores (not grades), and as **Wendell Wagner** has mentioned, IQ is not a particularly strong indicator of college performance. Your argument simply doesn’t have a leg to stand on.

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**Author:** ![BlinkingDuck](https://avatars.discourse-cdn.com/v4/letter/b/eada6e/32.png) [@BlinkingDuck](https://boards.straightdope.com/u/BlinkingDuck)\
**Post date:** [April 20, 2011, 6:12pm UTC](https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928/27 "2011-04-20T18:12:38Z")

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> [@CitizenPained](#):
>
> You couldn’t test my class since I only give As, Bs, and Fs.

When I taught college, they actually allowed minuses as in D- and had a weight of 0.7 for GPA (instead of 1 for a normal D). Sounds uncollegiate but I loved it. D- was actually a very common grade I would use in classes that students needed to take but would take no more (I taught math). I figured a D- would never fool anyone into thinking the student learned much but it would allow them to never attend a math class again 😃 So most common grades I would give out were B followed by C followed by D- then A then F.

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**Author:** ![notsoheavyd3](https://avatars.discourse-cdn.com/v4/letter/n/85e7bf/32.png) [@notsoheavyd3](https://boards.straightdope.com/u/notsoheavyd3)\
**Post date:** [April 21, 2011, 4:25am UTC](https://boards.straightdope.com/t/assuming-professors-curves-are-not-auto-spikers-but-normalizers-whats-the-average-distribution/578928/28 "2011-04-21T04:25:44Z")

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> [@BlinkingDuck](#):
>
> When I taught college, they actually allowed minuses as in D- and had a weight of 0.7 for GPA (instead of 1 for a normal D). Sounds uncollegiate but I loved it. D- was actually a very common grade I would use in classes that students needed to take but would take no more (I taught math). I figured a D- would never fool anyone into thinking the student learned much but it would allow them to never attend a math class again 😃 So most common grades I would give out were B followed by C followed by D- then A then F.

Man, I would have given my eye teeth if someone would have just cut me a break and given me a D- in French 4 when I was in college. (But oh no, we just can’t have that.) I would have promised to never take another class if they did.

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