I wrote to Testmasters regarding the inconsistency between the SI chart and Testmasters’ analysis of the 10,000 TX scores. Here are the questions and replies:
Tim Keehan says:
February 10, 2016 at 4:18 pm
This is terrific analysis, thanks for your hard work. I do have a question. Your projection of 219 for TX seems difficult to square with the PSAT/NMSQT “Understanding Scores 2015” SI chart, which places 219 well into the “99+” percentile, which is based on a national research sample. The SI chart would seem to place TX at 215-217. Can you explain the inconsistency?
Michael says:
February 10, 2016 at 4:38 pm
Hi Tim! Thanks for your kind words! There’s two things to note about the Understanding Scores chart put out by the College Board: 1) as you said, these scores are from a national sample while National Merit is awarded on a state-by-state basis. 2) it’s unclear where the 99+ scores differ, meaning no one knows where each fraction of a percent lies. A 99.5% could be just at a 214 and a 99.6% at a 215, or it could be that 214-220 could all be 99.5%. Note that the broad range of 99+’s is actually a new addition by College Board because if you take a look at this archived copy of the 2014 Understanding Guide, on page 3, CB simply lists 224-240 as 99+ without detailing each individual score in that range. I hope these two points clear up the questions you had about our post and the Understanding guide!
Tim says:
February 10, 2016 at 4:54 pm
Michael, thanks for your prompt response. I believe last year’s NMSF cutoff for Texas was 220 (below the 99+ percentile of the 224-240 range you cited). The projected 219 for this year would put Texas a number of rungs into the 99+ percentile. I can’t figure out why last year’s scores (and previous years as well) has Texas in the 99 percentile, four rungs below the 99+ mark, and this year’s projection of 219 has Texas six rungs into the 99+ percentile. That seems to be the inconsistency. Could the SI chart be wrong or somehow skewed (which would seem odd since the College Board possesses all the scores)?
Michael says:
February 12, 2016 at 1:48 pm
Hi Tim, we can’t necessarily comment on how College Board’s SI table was created, since all we know is the data we have. But if we’re speculating here, it’s possible that the SI table functions different than previous years’ because some values, namely odd selection index scores, are much more difficult to attain due to the way the selection index is set up. Because you’re summing the Reading, Writing, and Math test scores and multiplying by two, the only way you’ll get an odd value is if you got a XX.5 on the math section, which occur slightly more frequently than XX.0’s, especially near the low end. This can be seen visually in our graphs which show a “sawtooth” pattern where there are large jumps in between discrete values. As a result, the large range of SI values might be a bit more tightly grouped than it initially appears.
Hope this helps!
Would be interested to hear thoughts from the board.