In media mix research, the concept of synergy has become increasingly important (Assael, 2011). Positive synergy is created when the combined use of two or more media results in a more positive outcome (e.g., higher sales) than single-media use; negative synergy (cannibalization) occurs when single-media use leads to more positive outcomes than combined-media use. Synergy may occur when advertisers invest in multiple media to attempt to enhance the reach and/or the contact frequency of their advertising campaigns (e.g., Aravindakshan, Peters, & Naik, 2012; Raman, Mantrala, Sridhar, & Tang, 2012). Alternatively, synergy may be the result of consumers using different media, as a result of which they can be confronted with advertising in these media (e.g., Enoch & Johnson, 2010; Lin Venkataraman, & Jap, 2013; Schultz, Block, & Raman, 2012). This study investigates the latter, that is, synergies created by consumers' media usage.

Several authors have identified the measurement of interactions between media at the consumer levels as an important research topic (Enoch & Johnson, 2010; Pilotta & Schultz, 2005; Schultz et al., 2012; Wendel & Dellaert, 2005). Most studies on synergy due to consumers' media usage are experimental, exposing people to advertising stimuli in different media and measuring their responses in terms of attitudes and behavioral intentions (e.g., Danaher & Rossiter, 2011; Voorveld, Neijens, & Smit, 2011). These studies often include a single advertising campaign involving a single combination of media. Most of these studies have investigated the effects of combining two media (e.g., radio and television), only a few examined the combination of three or more media (e.g., Chatterjee, 2012). In addition, many of the existing studies suffer from a lack of ecological validity, as they are conducted under forced exposure conditions and measure responses immediately after ad exposure.