(From the test)

Note, however, that in this case we also need an explanation of why these test-takers ended up with factual beliefs which systematically favor a certain political position. The explanation closest at hand is that they have been given biased factual information (e.g., from the media). Thus in this case, too, the cause of the correlation is bias, but it does not stem from the test-takers themselves, but rather from the information that they are given.

Or media bias has a negligible effect, but people randomly encounter more of one side than the other. Do the scores follow a bell curve around no bias?