The conceptual foundations of consumer engagement build on relationship marketing theory ^[1][29]. For a company, a relationship orientation typically creates a competitive advantage, which in turn exerts a positive impact on its performance [2]. However, in addition to myriad types of engagement described in the marketing literature (e.g., brand engagement in self-concept ^[3][33], customer brand engagement ^[4][34] or consumer brand engagement ^[5][35]), definitions of engagement also abound. Hollebeek (2011) ^[6][4] construes engagement as the consumer’s level of motivation relative to the brand and their context-dependent state of mind, characterized by specific levels of cognitive, emotional, and behavioral activities. Brodie et al. (2011) ^[1][29] define engagement as a psychological state induced by consumer’s interactivity and co-creative experiences with the object. Although some definitions have aspects in common, scientific support on the nature of the concept of engagement in marketing is scant ^[7][8][36,37]. There is also a lack of consensus on the dimensionality of engagement ^[3][6][4,33]. Views diverge over the combination and number of dimensions and sub-dimensions involved in the process ^[9][38].

Some researchers view engagement in a one-dimensional way ^[10][11][12][39,40,41] (e.g., clicking on online content). Other scholars argue that brand engagement should be viewed instead as a manifestation of engagement rather than an operational definition of this concept ^[13][42]. However, studies show that to offer an exceptional engagement experience, multiple dimensions must be stimulated simultaneously ^[14][15][43,44]. The marketing literature demonstrates that engagement is commonly measured along three dimensions, cognitive, affective/emotional, and behavioral/activation (e.g., Lourenço et al., 2022 ^[16][45]; Hollebeek et al., 2014 ^[17][30]).

The cognitive dimension consists of information processing, i.e., the perception of a brand’s usefulness and relevance. It is measured by various sub-dimensions such as influence (experience), which refers to a brand’s impact (positive or negative) in a consumer’s life ^[18][19][46,47]. Absorption is another sub-dimension mobilized in studies of cognitive engagement ^[20][21][22,48]. According to the flow theory ^[22][49], the disposition of deep absorption in an intrinsically pleasurable activity leads to strong engagement. Another dimension related to the cognitive aspect is attention ^[6][23][3,4]. This is the degree of concentration relative to a brand. The higher it is, the more the consumer is engaged with the subject. Then, self-congruity ^[24][50] is used to measure the identity aspect of cognitive engagement. The consumer integrates the identity signal of a brand into his self-concept ^[25][51] which allows him to define himself by projecting a certain image to those around him ^[3][33]. In addition, self-congruence ^[24][50] is used to measure the identity aspect of cognitive engagement. The last sub-dimension is identification, which is when the consumer’s self-image overlaps with that of the brand ^[26][27][52,53], whether real, social, ideal, or social-ideal ^[24][50].

The affective dimension is based on emotional congruence with the brand characterized by enthusiasm ^[21][28][48,54] and pleasure ^[29][55]. The affective aspect also includes attachment. Derived from experiences, emotions, and expectations associated with a brand ^[30][56], attachment motivates individuals to engage in and adopt specific behaviors ^[31][57]. In addition, studies in psychology have found a positive correlation between engagement and personal well-being (e.g., ^[32][33][58,59]). The more engaged the individual is, the higher their life satisfaction ^[9][38].

The behavioral dimension represents the consumer’s activation towards the brand ^[17][30]. Various actions can be considered manifestations of engagement, for example word-of-mouth ^[34][60], compulsive buying ^[35][61], as well as participation and interaction/co-creation ^[28][54]. Indeed, past studies have underscored the importance of interactivity in the consumer-brand dyad, as it enables voluntary effort to maintain a level of interaction that elicits continued engagement (e.g., ^[1][7][29,36]). Obviously, through SM, the consumer is able to interact directly with the brand ^[36][62], faster than in an offline context ^[37][38][63,64]. By the same token, the conceptualization and operationalization of behavioral engagement underwent a major transformation during the 2000s.

SM have transformed the nature and practice of online communication into an extensive two-way dialogue between users ^[39][65] and brands. Digital technologies facilitate users’ social participation ^[40][66] and progressively build intimacy ^[41][67], thus engendering novel behaviors that establish new social norms ^[42][43][68,69]. However, consensus about what constitutes behavioral engagement on SM is lacking ^[44][70]. Some authors measure engagement by the number of brand followers ^[45][71], while others link it to specific actions (e.g., the number of “likes” of a post) ^[46][72]. On the other hand, obtaining “likes” is a low engagement action and brands want more engaged and active exchanges with their followers (e.g., a comment, a share) ^[47][73]. It is therefore essential to differentiate the levels of behavioral engagement in the digital context.

The Consumers’ online brand-related activities (COBRA) behavioral construct ^[46][48][72,74] provides a unifying framework for analyzing consumers’ activities related to a brand’s content on SM ^[49][26]. COBRA activities are classified under three dimensions corresponding to a path of gradual involvement ^[46][72]. The first level is consuming, which entails followers’ passive participation in online brand communities ^[50][75]. One such example is reading. The second level is contributing; it includes interaction with brand-related content ^[51][76], and is exemplified by sharing. The third level is creating, which includes publishing original brand-related content ^[52][77], e.g., create a story (The stories are an option of the application on IG which allows to realize ephemeral visual content (for a duration of 24 h) by identifying an influencer. It should be noted that behavioral engagement can even go as far as consumer devotion, i.e., the manifestation of his devotion to a brand with his network. Voluntary, this ambassador can influence consumers to the benefit or disadvantage of the adored brand ^[53][32].

The literature on engagement confirms both the complexity of the concept and its importance to brands. The dimensions identified underline the multifaceted nature of the subject and the variety of fields of research interest ^[54][78]. Table 1 presents the main consumer engagement measurement scales used in marketing. However, HB is not managed in the same way as an inanimate brand ^[55][79]. This confirms that the concept is not surfing on a “trendy” keyword and that having measurement tools capturing its specificities is necessary.

The HB is differentiated from traditional brands owing to its human aspect. The human brand is imbued with physical and social realities, prejudices, and limitations. Although the HB poses risks related to management of its image, it also offers advantages in terms of the potential to improve the returns on the brand ^[74][96]. In addition, the HB has a wider range of attributes than does an inanimate brand and can adapt to the circumstances surrounding it. The HB also has a significantly greater capacity for reciprocity with the consumer than a traditional brand ^[75][97]. The bond between an HB and a consumer is similar to interpersonal relationships, especially in SM ^[37][38][63,64]. Indeed, many followers develop a parasocial relationship with an influencer—an imaginary relationship of friendship or love towards a media person ^[76][77][98,99]. A parasocial relationship enhances the perceived credibility of the influencer and positively affects brand trust and follower behavior ^[78][100].

However, while HB is extremely powerful, it is also very risky. Indeed, he is not immune to the risks of adverse events such as illness or misconduct ^[74][96]. For example, in 2020, Maripier Morin (Quebec host, television columnist, businesswoman and actress) saw her empire crumble when she admitted to accusations of sexual harassment, physical assault and racist remarks. Her business partners could not appear in the scandalous image of the actress and host. She was dumped by the brands she represented. In addition, Bell Media and Videotron have removed its television programs on all their platforms ^[79][101]. The main dangers that the human body imposes on HB are mortality, hubris, unpredictability, and social entrenchment. These characteristics lend it a particularly high level of authenticity and resonance, which enhances its value from consumers’ standpoint ^[80][102]. This supports the importance of considering the living nature of HB when examining the engagement relationship ^[75][97].

As mentioned earlier, engagement in marketing has primarily been measured in the context of the consumer-brand relationship ^[81][103]. ThWe researchers aalso observe that the items used apply to the use of traditional brands and/or in specific and often offline contexts (e.g., engagement to art, ^[18][46]). Moreover, depending on the interests of the influencers, the engagement differs ^[82][31]. This calls into question the relevance of current measuring instruments for influencer on SM. Admittedly, scales applying to the context of SMs have been listed, but they are intended to measure engagement to platforms or websites ^[13][58][42,82], which is difficult to transfer to HB ^[17][83][30,104]. Additionally, the rapid consumption pattern on SMs ^[84][105] and two-way exchanges with SM suggest unique engagement process and behaviors that existing measurement tools do not capture. We Dtherefore conclude that due to the uniqueness of HB and the context under study, the available measurement tools are not applicable. The researchers We propose the development of the Influencer Engagement Scale on Social Media (IESM). Table 2 summarizes the dimensions and sub-dimensions of engagement with an influencer and Figure 1 presents the theoretical model.