st: Re: grading

[Christopher F Baum <baum@bc.edu>]

On Wednesday, June 11, 2003, at 02:33 AM, Chris wrote:

> Thanks.  I must still not understand how -pctile- and -xtile- work.  
> This code
> gave me sort of a U-shaped distribution of grades:  highest-scoring 
> students
> got fail, and so did the lowest-scoring.  In the middle were honors, 
> high pass,
> and pass.
I had the percentiles backward, given that the lowest percentiles will 
be the lowest grades.


> pctile gr = score, nq(20)
> xtile pc = score, cut(gr)
> g str9 grade="Fail"
> replace grade="Honors" if pc>17
> replace grade="High Pass" if pc>12 & pc<18
> replace grade="Pass" if grade=="Fail" & score>299
The 'gr' variable contains 20 observations, corresponding to the 5th, 
10th, 15th,... 95th
percentiles of the distribution. Thus the top 3 categories should be 
pc=18, 19, 20; the next five should be 13,..17.
The example you posted today contained rules not included in your 
original postiing (re 199, e.g.)

Kit

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