Halliday & Matthiessen (2014: 305):
However, the simple present also occurs in a more ‘relational’ sense of ‘expresses the opinion that’, as in She says she prefers cigarettes to fish. And when the Sayer is realised by a nominal group denoting a symbol source other than a human speaker, the tense selection is more likely to be more like that of a ‘relational’ clause, as in the study says that such a diversified village structure produces a dualistic pattern of migration. Here the ‘present in’ is unlikely: the study is saying that ... would not occur.* While such clauses are still clearly ‘verbal’, they are closer to ‘relational’ clauses than are ‘verbal’ ones with a human speaker as Subject.
* This is overstating the case, since the study is saying that ... could easily occur, especially in a spoken exchange where there is disagreement about what the study is saying.