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⁷ Bartels, ‘Messages Received’, p. 267. Indeed, only very few studies into media persuasion exist from the 1970s or 1980s. See, for example: Erikson, Robert S., ‘The Influence of Newspaper Endorsements in Presidential Elections: The Case of 1964’, American Journal of Political Science, 20 (1976), 207–233CrossRefGoogle Scholar; Coombs, Steven L., ‘Editorial Endorsements and Electoral Outcomes’, in Michael B. MacKuen and Steven L. Coombs, More than News: Media Power in Public Affairs (Beverly Hills, Calif.: Sage, 1981)Google Scholar; Wagner, Joseph, ‘Media Do Make a Difference: The Differential Impact of Mass Media in the 1976 Presidential Race’, American Journal of Political Science, 27 (1983), 407–430CrossRefGoogle Scholar.

⁸ Norris, ‘Did the Media Matter?’

⁹ Bartels, ‘Messages Received’.

¹⁰ John Zaller, ‘The Statistical Power of Election Studies to Detect Media Exposure Effects’.

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¹² Zaller, John, The Origins and Nature of Mass Opinion (New York: Cambridge University Press, 1992)CrossRefGoogle Scholar; Bartels, ‘Messages Received’, p. 276.

¹³ Erikson, , ‘The Influence of Newspaper Endorsements in Presidential Elections’, p. 207Google Scholar.

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¹⁷ Kim Fridkin Kahn and Kenney, Patrick J., ‘The Slant of the News: How Editorial Endorsements Influence Campaign Coverage and Citizens’ Views of Candidates’, American Political Science Review, 96 (2002), 381–394Google Scholar.

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¹⁹ The use of an overly simplistic dichotomy that divides the press into Conservative v. Labour papers may explain why an earlier study of the 2005 British general election found only limited persuasion effects on party and leader evaluations or vote choice, with some of the significant estimates even pointing in the wrong direction; see Norris, , ‘Did the Media Matter?’, pp. 210–213Google Scholar.

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²³ Druckman and Parkin, ‘The Impact of Media Bias’, p. 1031Google Scholar.

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²⁷ Dobrzynska et al. , ‘Do the Media have a Direct Impact on the Vote?’, p. 31Google Scholar; see also Lazarsfeld et al., The People's Choice; Kleinnijenhuis et al., ‘Issues and Personalities in German and Dutch Television News’.

²⁸ O'Keefe, Daniel J., Persuasion: Theory and Research, 2nd edn (Newbury Park, Calif.: Sage, 2002), p. 3Google Scholar. See also Walton, Douglas, ‘What is Propaganda, and What Exactly Is Wrong with It?’ Public Affairs Quarterly, 11(1997), 383–413Google Scholar, p. 394; and Garsten, Bryan, Saving Persuasion: A Defense of Rhetoric and Judgment (Cambridge, Mass.: Harvard University Press, 2006)CrossRefGoogle Scholar, pp. 2ff.

²⁹ Burnell, Peter and Reeve, Andrew, ‘Persuasion as a Political Concept’, British Journal of Political Science, 14 (1984), 393–410CrossRefGoogle Scholar, pp. 394–6.

³⁰ O'Keefe, ‘Persuasion’, p. 4.

³¹ O'Keefe, ‘Persuasion’, p. 5.

³² We selected seven of the largest and most prominent newspapers to provide a sample of the British media landscape that accounts for variation in newspaper type (broadsheets, red-tops and black-tops) and partisan tendencies (Labour and Tory papers as well as newspapers with more ambiguous endorsements like the Independent).

³³ For an extensive description of the data, see Brandenburg, Heinz, ‘Party Strategy and Media Bias: A Quantitative Analysis of the 2005 UK Election Campaign’, Journal of Elections, Public Opinion & Parties, 16 (2006), 157–178CrossRefGoogle Scholar.

³⁴ Elliott, Larry, ‘Why Alastair Campbell made Blair eat humble pie: Polls proved that only Gordon Brown could deliver a third Labour term’, Guardian, 21 April 2005, p. 26Google Scholar.

³⁵ Brandenburg, ‘Party Strategy and Media Bias’.

³⁶ See Kahn and Kenney, ‘The Slant of the News’.

³⁷ We standardized text lines because columns width tends to vary within and between newspapers. Our standardization procedure consisted of multiplying the number of text lines of any data entry with its observed column width and then dividing by the average column width across the entire dataset.

³⁸ This design also allows us to assess the impact of the sheer volume of positive or negative evaluations, or the trade off between positive and negative reporting (in other words, whether, e.g., 20 positive versus 20 negative statements have a comparable effect to that of two or three positive and negative points). These measures were included in initial analysis but require further exploration and are not included in the analyses presented here.

³⁹ The use of internet panels remains subject to criticism because of limitations in the sampling and selection procedures of some of these panels, which it is said might result in violations of analytical assumptions or possible bias in the findings. However, in an extensive survey comparison, the team of researchers that conducted the 2001 and 2005 British Election Study addressed most of the contentious issues. They argued that, while on the one hand sampling problems remain with internet surveys because internet access is not randomly distributed, internet surveys on the other hand address some core problems with face-to-face surveys, for example by eliminating interviewer effects. They also found that while marginal distributions of key variables differ across both types of survey, when estimating parameters in vote choice and turnout models, face-to-face and internet surveys yield remarkably similar results. Also, issues of over- or under-representation of social groups appear to be dealt with effectively through weighting procedures in internet surveys carried out by Yougov. See Sanders, David, Clarke, Harold D., Stewart, Marianne C. and Whiteley, Paul, ‘Does Mode Matter for Modeling Political Choice? Evidence from the 2005 British Election Study’, Political Analysis, 15 (2007), 257–285CrossRefGoogle Scholar. Most importantly, however, our aim is to assess possible attitude change through media effects, which does not require our sample of newspaper readers to be nationally representative. For this reason, the graphs presented below, as well as subsequent regression models, are based on data that are not weighted to reflect nationally representative readership figures.

⁴⁰ Because of an error in the programming of the questionnaire for Wave 1, respondents were not actually able to give parties a score of 10, but instead could only give a maximum score of 9. In our analysis, this is addressed by applying a scale factor to the Wave 1 scores.

⁴¹ Data included in our analysis comprise content analysis of op-ed pages only, since only these articles were coded for slant. The entire 2005 newspaper dataset is much larger and also contains content analysis of all news stories about the campaign (see Brandenburg, ‘Party Strategy and Media Bias’ for a description of the entire dataset).

⁴² Daily average tone scores were calculated from the coded text for each party in each newspaper (n = 26). Accordingly, the boxplots indicate the mean and quartile range calculated from twenty-six individual scores per party.

⁴³ van der Brug, Wouter and van der Eijk, Cees, ‘De campagne deed er toe, mediagebruik niet’, in Philip van Praag Jr and Kees Brants, eds, Tussen Beeld en Inhoud. Politiek en media in de verkiezingen van 1998 (Amsterdam: Het Spinhuis, 2000), pp. 214–242Google Scholar; van der Brug, Wouter and van der Eijk, Cees, ‘Welke effecten hadden de campagnes nu eigenlijk?’ in Kees Brants and Philip van Praag, eds, Politiek en Media in Verwarring. De verkiezingscampagnes in het lange jaar 2002 (Amsterdam: Spinhuis, 2005), pp. 244–267Google Scholar.

⁴⁴ In our content analysis of media channels, we also included evening news broadcasts on ITV and BBC. Since news broadcasts prove inherently more neutral than newspaper op-ed articles, the coding of television news differs from newspaper coding. In newspaper coding, any opinion voiced by anyone other than the author was not coded. However, television newscasts largely broadcast only such statements from party officials, experts or interviewed citizens, and therefore these statements were coded for partisan bias.

⁴⁵ Note that in a fixed effects model the first media indicator is automatically created, and is redundant. The second media indicator is hence most reflective of the media indicator variable in a fixed effects model. In multilevel literature, the procedure is often referred to as group-mean centering. Cf. Allison, Paul D., Effects Regression Methods for Longitudinal Data Using SAS (Cary, N.C.: SAS Institute, 2005)Google Scholar.

⁴⁶ For respondents interviewed during the first six days of the campaign, the average was based on the number of days in the campaign so far.

⁴⁷ These multicollinearity issues stem largely from the fact that a newspaper treatment of a party over the course of the campaign tends to be related to its treatment of the other parties.

⁴⁸ For Labour and the Conservatives, tone on these two parties has been included. For the Liberal Democrats, separate models including tone on Labour or the Conservatives were run. Note that exclusion of tone on a third party does not reduce the explanatory power of the model.

⁴⁹ Price, Vincent and Zaller, John‘Who Gets the News? Alternative Measures of News Reception and Their Implications for Research’, Public Opinion Quarterly, 57(1993), 133–163CrossRefGoogle Scholar, p. 158.

⁵⁰ Zaller, ‘Origins and Nature of Mass Opinion’.

⁵¹ At face value, it might seem desirable also to include non-readers as a control group whose opinion change over the campaign could serve as a baseline against which to assess media effects. Not only would this complicate the model specification but also, and more fundamentally, we are not proposing that readers as a whole are pushed in a direction different from that of non-readers. Rather, our models explain patterns of opinion change that result from specific media inputs – whether readers are actually persuaded by what their papers say. For that purpose, what matters are the differences in the messages readers are exposed to, and not any differences between the exposed and the unexposed.

⁵² Fournier, Patrick, Nadeau, Richard, Blais, André, Gidengil, Elisabeth and Nevitte, Neil, ‘Time-of-Voting Decision and Susceptibility to Campaign Effects’, Electoral Studies, 23 (2004), 661–681CrossRefGoogle Scholar.

⁵³ Both the random and fixed effects estimates were obtained using STATA's xtreg.

⁵⁴ Table 2 presents the model for Liberal Democrats with media tone on Conservatives as the second party. The model with media tone on the Labour party is presented in the Appendix.

⁵⁵ We imputed the mean income for those respondents who failed to report their income. Since this estimate is not significant as well, these respondents show no significant difference in evaluation of the various parties.