PSAT / NMSF cutoffs: Concordance tables vs. percentiles

Test Preparation
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I was looking at the CB website to see if there was any more guidance we might find helpful & noticed this (sorry if someone else already pointed it out): It is in the section of Info for Educators –

http://talk.collegeconfidential.com/sat-act-tests-test-preparation/1849640-national-merit-cutoff-predictions-class-of-2017.html#latest

“NMSC Selection Index
Counselors can approximate an NMSC Selection Index on the redesigned PSAT/NMSQT from pre-2015 PSAT/NMSQT scores. Use the “Section-to-Test” Concordance tables to convert the three subject test scores. Then, double the sum of the Reading, Writing and Language, and Math Test scores to calculate the approximate NMSC Selection Index.” (Concordance tables are here: https://collegereadiness.collegeboard.org/pdf/psat-nmsqt-preliminary-concordance-tables-2015.pdf)

As we can see there are “ranges” of possible SI’s that can be calculated this way on pg 3 but only 1 answer using pg 4 of the tables (my son’s would be 216). But each student has been assigned an SI which may be different than this calculation (my son’s actual is 218), so I wonder, what is CB’s messages to GC’s & schools by the note above?

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“As we can see there are “ranges” of possible SI’s that can be calculated this way on pg 3 but only 1 answer using pg 4 of the tables (my son’s would be 216). But each student has been assigned an SI which may be different than this calculation (my son’s actual is 218), so I wonder, what is CB’s messages to GC’s & schools by the note above?”

Computing all the outcomes in the range is the best way to figure out what the likely SI will be. Some outcomes occur more frequently than others.