[quote=Val]If you are referring to the very low percentage of students taking the SAT in some states, I think you may be seeing the effect of regional preferences for the ACT over the SAT.
And for the most part, only the kids who want to go to selective out-of-state schools take the SAT, if you live in an area where the local schools like the ACT. There's a ton of selection bias there.
Here's the analogous ACT chart:
http://www.act.org/newsroom/data/2011/states.htmlThe ACT is much less correlated to participation rates than is the SAT (-0.63 vs -0.89); I'd attribute that generally to more-selective schools requiring the SAT.
