Any insistence on "valid" and it will not exist.College Board and ACT did a concordance of combined SAT M/CR to ACT composite and even their table is riddled with caveats that it should not be relied on as anything other than a guide and likely does not reflect a true conversion for all test takers. Moreover it is now an "old" table, using figures from 2005 tests and thus cannot be considered applicable to 2011 tests. CB also shows a math to math and Cr to reading/Englieh conversion here from data from a 1990s study professionals.collegeboard.com/profdownload/pdf/rr9901_3913.pdf but its validity should be considered less than the math/CR to composite one that is more recent.
Also be aware of the following: Colleges that actually do any conversion usually use their own method of conversion which may not look anything like the ones you find on the internet and the conversions they do are often math to math and SAT CR to ACT English (not reading).
Last edited by drusba; 10-25-2011 at 05:28 PM.