The meaning of that sentence is not that there was only one study done on this topic though; just that the author is aware of that particular one, performed in

The meaning of that sentence is not that there was only one study done on this topic though; just that the author is aware of that particular one, performed in 1996, that makes the 85 percent claim. The use of 'one' here may even imply that the author is aware of more studies that confirm the usefulness of this technique, but that referring to more than this particular relevant source would be superfluous for this article.