PETER Costello believes the ABC is ''hostile territory'' for conservatives, but a study has found its television news leans towards the Coalition.

Economists Joshua Gans and Andrew Leigh made the finding in a research paper, How Partisan is the Press?, that also said that on another measure of bias The Age slants towards Labor.

The study of media from 1999 to 2007 found that television and talkback radio were most likely to lean to the right, while newspapers slant left. Overall, the media showed a slight inclination to the right.

The first part of the study involved subjecting a list of more than 100 public intellectuals to an analysis of mentions in Parliament to determine whether they were favoured by Labor (for example Michael Kirby and Mick Dodson) or the Coalition (Geoffrey Blainey, Helen Hughes).

The study then checked every reference to those public figures across 27 news services to calculate the media's slant. While for most outlets the statistical standard error made bias difficult to detect, ABC television news was significantly slanted towards the Coalition.