In contrast to risks that get nailed down, e.g. smoking and thalidomide, it describes risks that tend to hover indefinitely in the background and never seem to crystallize.
Phantom risks tend to arouse suspicion, but the carcass is never found.
The key to dealing with these risks lies in the procedures employed. Federal and state courts apply different rules to scientific evidence. The Federal Rules of Evidence are looked upon, however, as the benchmark for the admission of evidence in the courts. Before the Federal Rules of Evidence were codified, federal courts applied the Frye test. In contrast, the Federal Rules of Evidence, codified in 1975, appeared to set up looser requirements for admissible expert testimony.