I wonder if there is a distinct difference approach? between DEAF and Hard of Hearing attainment, it would be an error to assume 'like with like' as even a few more decibels holds a real key to attainment (As does reliance on non-standard ASL grammar approaches). As we are aware the USA has just a single Deaf University where such statistics can be be done with accuracy and state by state, each USA area has different approaches?
So you need TWO surveys. One hopes a neutral survey/research is undertaken without reference to the D/d being used randomly etc and correct identification of those surveyed. In the UK we don't usually link Hard of Hearing WITH members of the 'Deaf' community as they are two very different sectors, the old 'Deaf and HoH/HI' remit is obsolete.
There has been contention and criticism in the UK of researchers being led by the D/d thing but declared statistics then NOT differentiating when it comes to fact/identification who they are. The UK got 11 million stats attached to deaf people when that was a Hard Of Hearing statistic NOT a deaf one, and the official 'Deaf' stats are changed every time it is printed, anything from 15K to 150K! It is being allowed via 'inclusion' laws who officially are not drawing lines (i.e. NOT recognising the D/d thing, only in that people can hear or they cannot), as a result.
UK BSL activism was attacked for distortion and bias of research. Apparently exploiting the fact there are border-line hard of hearing who are deaf and who may even use some sign to suggest they are one and the same as the 'Deaf' community and culture, not just those border-line but a statistical 'carry on' to suggest ALL the same by inference, if not open declaration.
We could suggest the facts will still reveal poor literacy of English within the 'ASL Deaf' world, which will only lead to more of the 'blame' game instead of addressing WHY it happens, which is probably down to chaotic 'hashtag and activist-led' approaches to deaf education. There are no immersive sign approaches in the UK, some areas of the UK have no deaf schools either, there is no real evidence this has impacted on deaf literacy getting worse, indeed, it has improved considerably with mainstreaming and inclusive approaches.
There are constant challenges to BSL being an 'in' to English too or deaf sign users being really bilingual. As ATR reported recently there is still a UK reluctance to empower BSL in the classroom and this is paying off for the deaf child via increased literacy stats.