تبلیغات دو طرفه : یک فرا تحلیل

A meta-analysis is conducted that integrates empirical findings from the two-sided advertising literature. First, the study provides a summary of findings of the persuasive impact of two-sided advertising. Secondly, using regression analysis, the influence of message structure, marketer, and receiver variables on the persuasive impact of two-sided messages is tested. Finally, the crucial problem of the net-effect of source credibility and the amount of negative information on attitudes toward the brand is investigated. The results confirm that the persuasive impact of message sidedness depends on suggested variables (amount of negative information, attribute quality, placement of negative information, correlation between negative and positive attributes and marketers' voluntariness). Also the curvilinear relationship between the amount of negative information and brand attitude is supported.

Marketers traditionally present their products to consumers in a favorable light. However, sometimes marketers disclaim particular characteristics of their products in conjunction with asserting positive claims, thereby providing consumers with a two-sided argument in the advertising message. At first glance, mentioning negative aspects in an advertisement goes against common intuition, as the advertised product seems to be presented in an unfavorable light. However, there are situations when two-sided advertising can be applied as a useful advertising technique; this is particularly true when consumers already hold negative beliefs or attitudes about a brand, when they are exposed to attacking ads that comprise negative counterclaims about the brand provided by competitors, or when they receive unfavorable information provided by negative publicity. Given today's competitive communication environment, where advertisers are attacked by competitors or governmental authorities, there is an apparent need to understand the effectiveness of two-sided advertising more thoroughly. A variety of marketing studies suggest that product-related messages can indeed include some negative information and still be more effective than if no negative information is included, especially in terms of enhancing credibility. Unfortunately, previous results of two-sided advertising studies (with respect to other key dependent variables such as attitude toward the ad, attitude toward the brand, or purchase intention) deliver rather ambiguous findings and indicate a rather complex relationship between message sidedness and communication effects in marketing. Hence, profound knowledge on the effectiveness of two-sided advertising and influences of potential moderating and mediating variables is valuable to marketers in showing how communication strategies aimed at consumers can best be optimized. Furthermore, according to Crowley and Hoyer (1994), the research topic is also of theoretical interest, as the persuasive mechanisms of two-sided communication increase our knowledge of the basic communication and persuasion processes between marketers or policy makers and consumers.

Meta-analytic results confirm the general persuasive impact of two-sided messages taking all dependent variables together. The strongest impact was obtained for the effects size of perceived novelty such that two-sided messages significantly enhance the perceived novelty of the message. Also effects for source credibility are rather strong, followed by effects on cognitive responses. Two-sided messages significantly enhance the perceived credibility of the source and reduce negative cognitive responses. Furthermore, two-sided messages enhance brand attitude and purchase intention. Both effects are weaker than effects on source credibility and negative cognitive responses. The order of the strength of the effect sizes corresponds largely to the attribution model where two-sided messages enhance source credibility which in turn reduces cognitive responses and then enhances attitude towards the brand and purchase intention. The decrease in strength of the effects sizes is due to the non-deterministic relationship between the variables in the attribution model and also corresponds to the trade-off between source credibility effects and the effects of negative information investigated in our study. Weak but still significant effects emerge for positive cognitive responses and ad attitude: two-sided messages enhance positive cognitive responses; however, they reduce attitudes towards the ad which is also in line with the ambiguous impact of message sidedness. The heterogeneity of the integrative effect sizes of all dependent variables besides negative cognitive responses indicates the application of further variables contributing to the variability of the effect sizes. Hence, regression analysis was applied in order to resolve heterogeneity. We could resolve heterogeneity of the source credibility effect sizes but not for both attitudes measures and purchase intention. Regression results point to the correctness of the assumptions made about the effects of message structure and marketer variables, even though not all of the relationships achieved statistical significance and net effects had to be assumed. Particularly, results show that source credibility is enhanced by discounting experience or credence attributes, when the negative information is not placed first and when marketers make negative disclosures voluntarily. Attitude towards the ad is lowered by the amount and importance of negative information included, when the negative information is placed first and when the ad is transmitted via broadcast media. Attitude toward the brand and purchase intention is enhanced when negative attributes are correlated with positive attributes, negative information is placed last and more negative information is included. Mixed results came up for the number of measurement items: whereas the effects are strengthened by the number of items for source credibility and brand attitude measures which is in line with our assumption, the contrary effect applies to ad attitude measures. At first sight, also the positive effect of amount of negative information on brand attitude and purchase intention seems to be contradictory but can be explained by a trade-off between message sidedness and source credibility that affects attitude toward the brand. Here, a curvilinear relationship emerges depending on the proportion of negative information included in the two-sided message such that up to fifty percent of negative information with rather moderate importance does not diminish the positive credibility effects of two-sided messages on brand attitude.