The short answer is not much. At best, they may correlate to someone having a blood alcohol concentration over a .08. At worst, they prove nothing at all. To understand their meaning you must look at how they came into existence and who developed them.
In the late 1970’s, NHTSA (the National Highway Traffic and Safety Administration) paid for some research to see if tools could be developed for law enforcement to identify people who are potentially DUI / DWI.
There were several studies paid for by the government. Specifically, there are six primary studies relied on by law enforcement. However, none of the studies have been subject to peer review.
1977 Study (Not Peer Reviewed)
1981 Study (Not Peer Reviewed)
1983 Study (Not Peer Reviewed)
Colorado Study (Not Peer Reviewed)
Florida Study (Not Peer Reviewed)
San Diego Study (Not Peer Reviewed)
According to Wikipedia, peer review has been defined as:
...the process of subjecting an author's scholarly work, research, or ideas to the scrutiny of others who are experts in the same field. Peer review requires a community of experts in a given (and often narrowly defined) field, who are qualified and able to perform impartial review...Pragmatically, peer review refers to the work done during the screening of submitted manuscripts and funding applications. This process encourages authors to meet the accepted standards of their discipline and prevents the dissemination of irrelevant findings, unwarranted claims, unacceptable interpretations, and personal views. Publications that have not undergone peer review are likely to be regarded with suspicion by scholars and professionals.
Thus, the research has not been subject to scrutiny in the scientific community and begs the question why not? Only the government can answer this question.
So what does the government say these studies show? Unfortunately, much of law enforcement does not even know what their own research says. If you ask most officers who regularly conduct DUI investigations, they will tell you that field sobriety tests show “impairment.”
However, the government’s own research concludes this is not the case. If you are willing to accept these non-peer reviewed studies, then you may merely conclude that a poor performance correlates to a blood alcohol concentration above a .08. Moreover, the tests were previously used to show a blood alcohol concentration above a .10. Then the law changed in several jurisdictions, and somehow it also changed scientific results.
Consequently, even if you believe NHTSA’s own research, these agility tests do not show driving impairment.