The author treats testing positive as sufficient for having syndrome Q. But his premises say that it’s necessary: if someone does have syndrome Q, then they will test positive, not the other way around. So Justine might not have syndrome Q, even though she tested positive.

The author claims that the test is accurate and positive when someone does have syndrome Q. He doesn’t necessarily need to provide scientific justification for this, but he does say that research has proven it to be true.

Instead, the author fails to distinguish between a person testing positive for syndrome Q and that person having syndrome Q. He doesn’t mistake a person not having syndrome Q with that person not testing positive for it.

The author never confuses his claim about the test’s overall accuracy with his claim about Justine’s test. Also, we have no reason to believe that the research used an “arbitrary group” when measuring the test’s accuracy.

If someone does have syndrome Q, then they test positive. So the test does have reliable results for the presence of syndrome Q. We don’t know whether it has reliable results for the absence of syndrome Q, but regardless, the author never confuses the ideas presented in (E).