Introduction
Due to its dynamic and emergent nature, the effectiveness of social media as a marketing communications channel has presented many challenges for marketers. It is considered to be different to traditional marketing channels, and even other digital marketing channels, centring around a two-way conversation or exchange (Bacile, Ye and Swilley, 2014; Shih, 2009). Many organisations are investing in their social media presence because they appreciate the need to engage in existing social media conversations in order to protect their corporate or brand reputation (Lee and Youn, 2009), increase customer engagement (Gummerus, Liljander, Weman and Philstrom, 2012) or increase online sales (Tsimonis and Dimitriadis, 2014). As organisations increasingly develop their social media presence, it is vital to be able to evaluate the impact of this investment, including its contribution to achieving marketing objectives, as well as more generally understanding any return-on-investment (ROI) (Pang and Lee, 2008; Fisher, 2009; Kumar and Mirchandani, 2012; McCann and Barlow, 2015).