Converting SAT and ACT to IQ

I. A search of ‘SAT to IQ’ on google results in being presented with the website ‘iqcomaprisonsite.com’, which uses this table:

1. He used the mean and SD to calculate the percentiles, while I took the percentiles straight from the table. This does lead to some difference at the high end, with his method yielding a z-score of 2.95 for a perfect SAT score, while mine yields a z-score of 3.29.
2. I used a regression coefficient of 0.84 while he used a coefficient of 0.8. The difference is negligible, and not worth discussing with the current amount of evidence.

Beyond this, I had to make some quick and dirty statistical adjustments. For instance, some of the SAT scores share a percentile, so I had to space out the percentiles manually by assuming that the distance in percentile between the scores was equal. For instance, if 1390 and 1400 share the 92nd percentile, I assign 1390 a percentile of 91.83 and I assing 1400 a percentile of 92.16. Also, due to the greater numeric spacing between ACT scores, I had to fill in the empty spaces with the nearest score.