We find no evidence that partisan newspapers affect party vote shares, with confidence intervals that rule out even moderate-sized effects.
That is the conclusion of this paper,the effect of newspaper entry and exit on electoral politics.
Produced by three American academics,it looks at American daily papers from 1869-2004,it finds that newspapers can have a robust effect on turnout but that there was little or no evidence of partizan newspapers affecting shares of the vote.
Neither did the study find anty correlation between the affects on incumbents in roles either helping or hindering them.
The results they say are consistent with the model that says that newspapers affect the political process mainly by providing information.Where there is little information,there is a lower turnout in the political process.