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 Post subject: Class Rank Estimator
PostPosted: Thu Jun 16, 2011 2:35 pm 
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This is a method of estimating your class rank based off of various data points. Linked below is an online calculator that should be fairly intuitive to use, and I have also left formulas behind which can be plugged into Excel (in case the calculator goes down).

Estimator mechanics:

This is an estimate based off the assumption that your school's GPA distribution is roughly "normal" ("normal" distributions being a specific, common type of distribution whose characteristics are likely to match your school's grade distribution). The estimator utilizes two data points to figure out what your school's grade distribution looks like, and then uses that estimate of your school's grade distribution to tell you where you rank, based upon your GPA.

The first data point the estimator needs can be any ranked data point except for the median (e.g. 3.5 is top 25%, or 3.1 is bottom 25%). The second data point the estimator needs is the median GPA (if you don't have the median GPA, the mean should be pretty much the same number, assuming your school has a normal distribution).

I should stress that this will yield only an estimate, though I think it should be fairly accurate (unless you're an outlier of sorts, either high or low. It is likely to be less accurate for outliers).



Online Calculator, graciously made by LSATSCORES2012

http://mylsn.info/class_rank.php



Excel code:

Open excel and follow these directions:

Cell A1: enter your GPA
Cell A2: enter the median gpa at your school.
Cell A3: enter the GPA of a certain ranked data point (e.g. 3.7 is ~ top 6.8% at UVA, so someone from UVA would enter 3.7)
Cell A4: enter the rank of that GPA (e.g. enter 6.8 if you're at UVA).
Cell A5: copy and paste this formula:

=(1 - NORMDIST(A1, A2, (A3 - A2)/NORMSINV(1-(A4/100)), TRUE))*100

Press enter. Whatever comes up in A5, you're in the top that percentile. You can save the sheet and use it later, as well.





The majority of the replies below are people I estimated for using the manual workaround, until we figured out a way to just put the calculator online. After that there's a little discussion about the calculator and various requests for estimation.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 3:41 pm 
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Posts: 5
I'll give it a go.

Mean: 2.91
Top 33%: 3.06

Estimate: 3.35, 3.21, and 3.56

Let's see what you got, you math magicians, you!


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 3:41 pm 
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Median: 3.3
37.5%: 3.42
12.5%: 3.68

Estimate the following GPAs: 3.49, 3.73, 3.81.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 3:54 pm 
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Posts: 2999
I wish I could partake in this.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 3:56 pm 
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PolemisLopez wrote:
I'll give it a go.

Mean: 2.91
Top 33%: 3.06

Estimate: 3.35, 3.21, and 3.56

Let's see what you got, you math magicians, you!


Top 9.8%, 18.9%, and 2.8%.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 3:58 pm 
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Joined: Tue Jun 07, 2011 9:04 am
Posts: 8
great thanks


Last edited by skrillo on Tue Jun 21, 2011 2:35 pm, edited 1 time in total.

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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:00 pm 
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traehekat wrote:
Median: 3.3
37.5%: 3.42
12.5%: 3.68

Estimate the following GPAs: 3.49, 3.73, 3.81.


Top 30.7 (28.3), 12.7 (9.7), and 8.8 (6.1).

The grade distribution at your school isn't perfectly normally distributed, so the number in parenthesis is the estimation based off the 12.5 percentile. I'd probably trust the 12.5% estimator for the grades near it, while I'd trust the 37.5 estimate for the grades near that.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:09 pm 
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Joined: Sat Sep 19, 2009 4:13 pm
Posts: 174
3.33 median
top 10% 3.71

estimate 3.727

thanks so much for this!


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:11 pm 
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shadow. wrote:
3.33 median
top 10% 3.71

estimate 3.727

thanks so much for this!


Top 9%. No problem.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:15 pm 
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Posts: 70
10% 3.612
25% 3.370
33% 3.212
50% 3.064

Where would 3.819 fall? Approx Class size: 240


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:18 pm 
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squ1rtle wrote:
10% 3.612
25% 3.370
33% 3.212
50% 3.064

Where would 3.819 fall? Approx Class size: 240


Top 3.9% using the 10% as an estimator. Awesome job, congrats.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:35 pm 
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Joined: Thu Oct 22, 2009 3:05 pm
Posts: 146
Class Size = 250
Median = 3.09
Top 33% = 3.30
Top 25% = 3.37
Top 20% = 3.49
Top 10% = 3.71

Guess:

3.28
3.76
3.45
3.92


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:36 pm 
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Joined: Sat Feb 05, 2011 3:01 am
Posts: 60
Thanks for this public service.

Last year's #s at UC-Tenderloin:
top 15% 3.542
top 20% 3.458
top 25% 3.396
top 30% 3.335
top 35% 3.281
top 40% 3.223
top 45% 3.173
top 50% 3.131
top 75% 2.858

I don't know the mean. If it helps, that year's class had ~470 students. This year's has ~370.

How about 3.704?


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:40 pm 
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Posts: 19009
FireNextTime wrote:
Thanks for this public service.

Last year's #s at UC-Tenderloin:
top 15% 3.542
top 20% 3.458
top 25% 3.396
top 30% 3.335
top 35% 3.281
top 40% 3.223
top 45% 3.173
top 50% 3.131
top 75% 2.858

I don't know the mean. If it helps, that year's class had ~470 students. This year's has ~370.

How about 3.704?


No problem. I'm just going to guess that your mean is the same as the median, which is a fairly sound assumption.

Using the top 15% as the estimator, you are in the top 7.4%. Congrats!


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:44 pm 
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Joined: Wed Oct 22, 2008 11:08 am
Posts: 19009
mebeSajid wrote:
Class Size = 250
Median = 3.09
Top 33% = 3.30
Top 25% = 3.37
Top 20% = 3.49
Top 10% = 3.71

Guess:

3.28
3.76
3.45
3.92


34.5%
8.3%
22.4%
4.3%


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:47 pm 
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I started making an excel spreadsheet for kicks, but I hit a speed bump at the final step. Is there a way to calculate the p from the z score with a formula in excel? My stats memory is a little fuzzy...

Heres what I have so far
https://spreadsheets.google.com/spreads ... n_US#gid=0


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 4:48 pm 
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NYC Law wrote:
I started making an excel spreadsheet for kicks, but I hit a speed bump at the final step. Is there a way to calculate the p from the z score with a formula in excel? My stats memory is a little fuzzy...

Heres what I have so far
https://spreadsheets.google.com/spreads ... n_US#gid=0


Very nice. This is actually how I've been doing it, but I wasn't sure on how to put it in an online format. If you use the norminv function you'll be able to do everything else easily.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 5:09 pm 
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Joined: Thu May 26, 2011 3:33 pm
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dailygrind wrote:
NYC Law wrote:
I started making an excel spreadsheet for kicks, but I hit a speed bump at the final step. Is there a way to calculate the p from the z score with a formula in excel? My stats memory is a little fuzzy...

Heres what I have so far
https://spreadsheets.google.com/spreads ... n_US#gid=0


Very nice. This is actually how I've been doing it, but I wasn't sure on how to put it in an online format. If you use the norminv function you'll be able to do everything else easily.


Thanks, the spreadsheet should be able to tell you your rank now.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 5:12 pm 
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Joined: Tue Aug 11, 2009 4:31 am
Posts: 208
edit


Last edited by timertimer61 on Fri Jul 08, 2011 10:18 pm, edited 1 time in total.

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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 5:13 pm 
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Joined: Wed Oct 22, 2008 11:08 am
Posts: 19009
NYC Law wrote:
dailygrind wrote:
NYC Law wrote:
I started making an excel spreadsheet for kicks, but I hit a speed bump at the final step. Is there a way to calculate the p from the z score with a formula in excel? My stats memory is a little fuzzy...

Heres what I have so far
https://spreadsheets.google.com/spreads ... n_US#gid=0


Very nice. This is actually how I've been doing it, but I wasn't sure on how to put it in an online format. If you use the norminv function you'll be able to do everything else easily.


Thanks, the spreadsheet should be able to tell you your rank now.


You sure? I was messing around with random UVA numbers and it kinda died on me. The major problem occurred when I tried to use a top 6.8% cutoff rather than a whole number.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 5:15 pm 
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Joined: Thu May 26, 2011 3:33 pm
Posts: 2215
dailygrind wrote:
NYC Law wrote:
dailygrind wrote:
NYC Law wrote:
I started making an excel spreadsheet for kicks, but I hit a speed bump at the final step. Is there a way to calculate the p from the z score with a formula in excel? My stats memory is a little fuzzy...

Heres what I have so far
https://spreadsheets.google.com/spreads ... n_US#gid=0


Very nice. This is actually how I've been doing it, but I wasn't sure on how to put it in an online format. If you use the norminv function you'll be able to do everything else easily.


Thanks, the spreadsheet should be able to tell you your rank now.


You sure? I was messing around with random UVA numbers and it kinda died on me. The major problem occurred when I tried to use a top 6.8% cutoff rather than a whole number.


I used a mini z table and 6.8 wasn't included. 6.8 has been added, so try it now.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 5:15 pm 
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Joined: Wed Oct 22, 2008 11:08 am
Posts: 19009
timertimer61 wrote:
class size: about 450
median: 3.3
1/3: 3.41
25%: 3.46
10%: 3.61

3.49; 3.59; 3.69.

also would i be able to know what rank # i am?


21.2%
11.5%
5.3%

and yeah. Take the class size and estimate from the percentage.


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 5:18 pm 
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Joined: Tue Aug 11, 2009 4:31 am
Posts: 208
dailygrind wrote:
timertimer61 wrote:
class size: about 450
median: 3.3
1/3: 3.41
25%: 3.46
10%: 3.61

3.49; 3.59; 3.69.

also would i be able to know what rank # i am?


21.2%
11.5%
5.3%

and yeah. Take the class size and estimate from the percentage.

oh yea duh...i suck at math as you can see lol


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 5:19 pm 
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NYC Law wrote:
I used a mini z table and 6.8 wasn't included. 6.8 has been added, so try it now.


Oh, I think I see how you're doing it. Did you use normsinv? I forgot to include the "S" when I posted about it, so I'd understand if you didn't. The formula's straightforward:

=(data point gpa - mean gpa)/normsinv(1-(data point rank/100)


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 Post subject: Re: ITT: Someone estimates your class rank.
PostPosted: Thu Jun 16, 2011 5:19 pm 
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Joined: Tue Nov 02, 2010 11:24 am
Posts: 2274
NYC Law wrote:
I started making an excel spreadsheet for kicks, but I hit a speed bump at the final step. Is there a way to calculate the p from the z score with a formula in excel? My stats memory is a little fuzzy...

Heres what I have so far
https://spreadsheets.google.com/spreads ... n_US#gid=0

haha cool


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