The defence and the rebuttable presumption had been two different things.

Two cases in the 1980s had demonstrated that the rebuttable presumption was an anachronism.

There may be a rebuttable presumption that pneumoconiosis resulted from such employment for miners long-term employed at one or more coal mines.

However, many modern cases have found merger clauses to be only a rebuttable presumption.

There are two types of presumption: rebuttable presumption and conclusive presumption.