Whereas some professionals may have months to years to develop and maintain a trusting relationship (e.g., teachers, coaches, clinicians), in some professional settings, only a few minutes are oftentimes available to develop trust. For instance, in the United States, the average medical doctor's visit lasts approximately 17 minutes (Tai-Seale et al., 2007), and salespeople, who may ask the client to make a large monetary investment, may have less than that (Soorjoo, 2012). In such cases, the tactics employed to generate trust must be communicated quickly and effectively. A question is whether the behaviors recommended to build trust differ between those professions in which trust must be built quickly versus those in which longer periods of time are available.

A critical element of compliance is the magnitude of the initial request (e.g., Brown & Levinson, 1978). Request can vary in magnitude from the trivial (e.g., "Have a seat.") to the large (e.g., "Set my client free."). Requests made in a hospital or a courtroom may involve a large request (e.g., "Undergo this painful procedure," "Sentence the defendant to death") that may require the development of trust to a point that such a request could be made with a reasonable expectation that it will be followed. Compared to the everyday compliance requests from friends and family (e.g., "Join us for a drink after work," "Put the kids to bed?", "Give me a ride to the airport?"), requests from professionals are often made without the benefit of strong existing trust and are thus more prone to fears of exploitation. Without trust, a doctor's referral for an invasive surgery may be seen unnecessary or as a "money grab," or a salesperson's recommendation for an expensive purchase as a shameless pursuit of commission.

There is an inverse relation between the magnitude of a request and compliance, such that compliance rates fall as the size of the initial request grows (e.g., Schwarzwald et al., 1979). However, the presence of trust can increase the size of the initial request that will be fulfilled (Kurzban, 2001; Wexley et al., 1975). Thus, an ancillary issue is whether those professions that more commonly make large requests recommend different behaviors than those professions that make smaller requests (e.g., teachers, professional colleagues).

Status may also affect the strategies people use to build interpersonal trust. People who hold a higher status position (i.e., employers, coaches, managers), versus those in a lower status position (i.e., employees, players), might display different nonverbal behaviors to build trust. For example, head nodding is used more by students toward their instructors than toward their peers (Helweg-Larsen et al., 2004). But the question here is, does the set of behaviors recommended for developing trust change depending on the sender's status relative to the recipient?

A critical question is whether these disciplines can be considered distinct. A conclusion based on identifying differences among disciplines would be moot if the textbooks each cited and built discussions based on the same small number of seminal sources.

Evidence indicates that the various disciplines drew primarily from their own discipline. The average number of references describing the use of or definition of behavioral displays per textbook was 3.35 (SD = 5.31, min = 0, max = 30), with clinical textbooks citing the most (M = 5.63, SD = 4.84) and coaching texts citing the fewest (M = 0.43, SD = 0.53). The proportion of citations from disciplines outside their own discipline varied across fields. Across all disciplines, 44% of citations were derived from their own discipline. For instance, in medical textbooks, 49 of the 73 references (67%) cited sources published in medical journals (e.g., Journal of General Internal Medicine, Medical Care, Journal of the American Medical Association). Alternatively, for education, 23 of 71 references (32%) came from education-based sources (e.g., Communication Education, Educational Leadership). Leadership texts featured the lowest proportion of citations from its own domain with 2 out of 24 (8%), and coaching textbooks provided the fewest total citations (3 total citations across 7 textbooks) and only one of these citations came from sport-related literature (Successful Coaching).

However, and importantly, across disciplines, a large portion of the sources were not cited by any other textbooks examined (85%), suggesting a low degree of overlap. When considering whether the impact of common citations, two authors from psychology and communications, namely, Albert Mehrabian (e.g., Mehrabian, 1972; Mehrabian & Ferris, 1967) and Edward Hall (e.g., Hall, 1963, 1966) were cited across several disciplines (e.g., education, law, and leadership). However, if the influence of those specific authors were removed from analyses, it would have little effect on the specific behaviors mentioned. Rather, these citations were used to define nonverbal communication and underscore the ubiquitous nature of nonverbal communication displays. Taken together, the data suggest that although textbooks did cite other fields, those citations did not meaningfully contribute to their list of recommended behaviors.

To assess the frequency with which specific behaviors were mentioned within the textbooks, a "yes" or "no" score was given for each textbook for each behavior. Frequency counts were tabulated for each discipline across each behavior. To examine more closely the relevant research questions, chi-square tests were used. Specifically, when different disciplines were compared, chi-square tests of independence were used. Alternatively, chi-square tests for equal proportion were used to test whether the behavior was mentioned more or less than chance (i.e., 50%). Fisher p-values were reported when no a priori predictions were made.

Fifteen of the 21 medical textbooks mentioned specific behaviors in which medical professionals should engage during meetings with clients. On average, they mentioned 5.87 behaviors (SD = 2.40). As noted in Table 2, the medical textbooks largely agreed on the importance of consistent eye contact with the patient (13 of 15 textbooks), a pattern different from chance χ²(1) = 8.07, p < .01. Textbooks also noted that professionals should lean toward their patients (11 of 15 textbooks), nod their head when listening (8 of 15), and make physical contact with the patient (10 of 15). Leaning forward, head nodding, and physical contact were not mentioned at a rate different from chance, χ²(1) = 3.27, p = .07, χ²(1) = 0.07, p = .80, and χ²(1) = 1.67, p = .19, respectively.

Medical textbooks provided several interrelated reasons as to why medical professionals should engage in trust-producing behaviors with patients. Specifically, they should build trust to understand their complaints completely (e.g., Fortin & Smith, 2012) and to ensure that the patient complies with the professional's treatment recommendations (Hart, 2010; Kim et al., 2004). Furthermore, textbooks stressed that active listening—which is a process through which the listener better understands the speaker's perspective and indirectly communicates this understanding back to the speaker (Rogers et al., 1957)—was fundamental to (a) an effective therapeutic relationship (e.g.,Bickley et al., 2007; Hart, 2010; Myerscough & Ford, 1996), (b) the establishment and development of trust (e.g., Fortin & Smith, 2012; Hojat, 2006), and (c) the ability to be empathetic to the needs of the client (e.g., Hojat, 2006; Polack & Avtgis, 2011; Roter & Hall, 2006).

Medical textbooks specifically spoke to the importance of head nodding. The textbooks' description of head nodding aligns with the larger literature on the topic. Specifically, head nods serve an important function to help regulate social interactions (McClave, 2000; Osugi & Kawahara, 2018) by demonstrating (a) agreement with the listener and (b) that the person is listening and understands their concerns (J. R. Anderson, 1985; Mehrabian, 1972). Head nodding was mentioned by at least 22% of the textbooks for each discipline, except for law, which did not mention it at all. This variability of head nodding across disciplines was unlikely to occur by chance, χ²(7) = 14.72, Fisher p = .02. On the one hand, the literature was clear that head nodding is associated with active listening and better provider-client relationships (Malisz et al., 2016). On the other hand, some research views head nodding as a form of submission (e.g., Eibl-Eibesfeldt, 1972; Morris, 1977), akin to a miniature bow, which may have reduced its recommended use in domains that stress the importance of expertise or high status.

Smiling was mentioned less frequently by medical textbooks than other disciplines. Smiling was mentioned by 20% of medical textbooks but was mentioned by 69% of education texts and 64% of sales texts. The recommendation of smiling is a pattern unlikely to emerge through chance, χ²(7) = 19.83, Fisher p < .01.

Eleven of 18 law textbooks (61%) provided guidelines for which behaviors should be communicated in the courtroom. Each textbook mentioned an average of 3.82 behaviors (SD = 1.33). The textbooks largely agreed on the importance of several behaviors, including maintaining an appropriate level of eye contact, creating verbal pauses during arguments (e.g., silence), and maintaining an appropriate physical distance from the judge and jury box.

Textbooks emphasized that the attorney's goal is to be viewed as trustworthy (C. H. Rose, 2011), honest (Rieke & Stutman, 1990), sincere (Findley & Sales, 2012), and that they should engage in various behaviors to demonstrate that they have "nothing to hide" (Berger et al., 2015). To facilitate this goal, eye contact (mentioned by 9 of 11 textbooks) was referenced more than chance, χ²(1) = 4.45, p = .03. Eye contact was mentioned more often than all of the other core behaviors, X²’s(1) ≥ 6.60, Fisher p's ≤ .03, except for physical distance which was not mentioned at a different frequency, χ²'s(1) = 4.70, Fisher p = .08. For textbook authors, eye contact was critical because it conveyed "belief, sincerity, and commitment" (Findley & Sales, 2012) and creates a "personal connection" with the jury (Read, 2007, p. 93). Five textbooks mentioned using an open posture (uncrossed arms and legs, open hands/palm exposed) as a cue to develop trust, a frequency unlikely to occur by chance, χ²(1) = 6.55, p = .01. These textbooks were specific regarding how such nonverbal behaviors could be used in conjunction: C. H. Rose (2011), for instance, proposed that attorneys should speak with an open posture, which when paired with silence while dropping one's arms and exposing one's body, gives "power" to the speaker by capturing the jury's attention.

Two behaviors advocated by other disciplines, mimicry and physical touch, were not mentioned for attorneys. Indeed, the pattern of mentioning for physical touch and mimicry across all the disciplines is unlikely to emerge through chance, χ²(7) = 20.04, Fisher p < .01 and χ²(7) = 40.07, Fisher p < .001, respectively. Law textbooks mentioned physical touch less frequently than education and medicine, χ²'s(1) ≥ 5.34, Fisher p’s ≤ .04, but not differently than sales, coaching, clinical, business, and leadership (which also did not mention physical touch), χ²'s(1) ≤ 4.90, Fisher p’s ≥ .05. For mimicry, law textbooks mentioned it less frequently than clinical, medicine, and leadership, χ²'s(1) ≥ 5.24, Fisher p’s ≤ .04, but not differently from education, sales, business, and coaching (which also did not mention mimicry), χ²'s(1) ≤ 5.41, Fisher p’s ≥ .05. As discussed later, mimicry is generally an interpersonal behavior and most effective in private one-on-one interactions in which both persons are actively participating (see Chartrand & Van Baaren, 2009). With respect to physical contact, a critical reason for its omission is legal: Most jurisdictions prohibit attorneys from physically touching jurors or judges.

Law textbooks, however, did place an emphasis on how behavioral expressions could both develop trust and convey expertise. Textbooks emphasized that attorneys are encouraged to exude confidence, power, and status (Findley & Sales, 2012), such that the attorney's disposition must always communicate "forthright confidence and belief in the strength of the case" (Murray, 1995, p. 78). "A lawyer whose body language lacks confidence or certainty is unable to be persuasive" (Haydock & Sonsteng, 2015, p. 27). Behaviorally, attorneys were instructed to sit in a relaxed position to demonstrate their confidence (e.g., "arm position asymmetry, sideways lean, leg position asymmetry, hand relaxation, neck relaxation, slight reclining angles," Suggs & Sales, 1978, as cited in Findley & Sales, 2012, p. 111).

Eleven of 12 sales textbooks recommended a set of nonverbal behavior, and those textbooks mentioned an average of 6.73 (SD = 2.69) behaviors. Of the behaviors mentioned, 54% were the "core" behaviors, including maintaining sufficient eye contact (to convey sincerity, R. Anderson et al., 2014; Ingram et al., 2012), nodding one's head while listening to the client, smiling, maintaining an appropriate physical distance, and leaning forward. In addition to the "core" behaviors, these textbooks also recommend sitting with an open posture and crossing one's legs in an open position (to indicate cooperativeness), and modulating the volume of one's voice (to emphasize key points and to force clients to lean in to hear critical information; Lill & Lill, 2008).

There was a clear consensus regarding the function that such nonverbal behaviors serve. Nonverbal behaviors are communicated to establish a "good relationship" (e.g., Lill & Lill, 2008), in which clients can communicate their needs and understand that the salesperson is there to help (e.g., Futrell, 2008; Johnston & Marshall, 2010), produce trust (Marks, 1991), and build rapport (Cant & van Heerden, 2004). Whereas there may be the belief that a good salesperson talks extensively to demonstrate their expertise and enthusiasm about their product, some textbooks stressed the opposite strategy, in which listening is the key to both understanding what the buyer wants and to the development of trust and rapport (e.g., Castleberry & Tanner, 2011; Johnston & Marshall, 2010; Marks, 1991). Indeed, one textbook stated that "good relationships" were based on the so-called "80/20 rule," in which salespersons listen 80% of the time and talk for 20% (Castleberry & Tanner, 2011). In this way, the nonverbal behaviors mentioned for being a good listener were the same behaviors used to develop trust. For instance, silence was mentioned not only as part of being a good listener, but it was cited repeatedly as crucial to the development of trust (e.g., Castleberry & Tanner, 2011; Jones et al., 2006; Marks, 1991), such that it allows time for the client to process information (Lill & Lill, 2008).

Moreover, nine of the 11 textbooks mentioned regulating the amount of distance between persons, a pattern unlikely to occur by chance, χ²(1) = 4.46, p = .03. The regulation of physical distance between people, and its relation to trust and attraction, has a long history in psychology and communication research (e.g., Argyle & Dean, 1965; Hayduk, 1978; Kleck, 1969; Little, 1965; Lott & Sommer, 1967; Mehrabian, 1968a, 1968b; Patterson & Gullion, 1968; Sally, 1995), and the textbooks' descriptions of the role of physical distance aligns with the larger empirical literature.

Eight of 12 clinical textbooks mentioned nonverbal behaviors, and of those texts, they mentioned an average of 7.75 (SD = 3.88) behaviors. There was tremendous agreement across the clinical textbooks, both in terms of each behavior's proposed importance and the recommendations for how to act. The importance of engaging in various nonverbal behaviors focused on creating an environment in which clients felt free to communicate (Ivey et al., 2010; Sommers-Flanagan & Sommers-Flanagan, 2015), felt safe and comfortable (Hill, 2009), in which clinicians can grow empathic and trusting relationships (Ivey et al., 2010), and express intimacy and provide feedback (Beier & Young, 1998). As noted in Table 2, the textbooks generally agreed on the importance of several behaviors, including eye contact, nodding one's head, smiling, maintaining physical proximity, mimicry, and leaning forward.

The across-textbook agreement was evident by inspecting two behaviors: eye contact and mimicry. Eye contact was mentioned by six of the eight textbooks, though this frequency was not different from chance, χ²(1) = 2.00, p = .15. Clinical textbooks claimed that eye contact is (a) critical given its importance to regulating the intensity of social interactions (Hill, 2009), (b) is used to communicate the clinician's interest and that they want to hear what the client has to say (Egan, 2002), and (c) a part of a larger strategy to produce "facilitative" relationships that contribute to positive evaluations of clinicians (Cormier et al., 2003). These mechanisms align with the larger literature on the role of eye contact. Eye contact is widely considered to be the "gateway" behavior to the development of trust. Eye contact's importance begins with its ability to focus attention (Cappella, 1981; Posner, 1980), and can thus be used functionally to change the social distance between people (Andersen, 1979; Mehrabian, 1969), strengthen interpersonal trust, and deepen levels of intimacy (e.g., Jones et al., 2006; King et al., 2011; Mason et al., 2005; Vuilleumier et al., 2005; Wyland & Forgas, 2010).

For mimicry, five of the eight clinical textbooks mentioned its importance for developing trust, though this frequency was not different from chance, χ²(1) = 0.17, p = .68. Mimicry—which may be accomplished by something as simple as changing one's speech rate to match the client's rate or leaning in to align with the client's lean—produces a "connection" between the client and the clinician (Brems, 2001; Hill, 2009) and is used to heighten the clinician's understanding of how their clients see the world (Cormier et al., 2003; Ivey et al., 2010). Such descriptions are consistent with the importance the broader literature places on mimicry. The broader empirical literature concludes that mimicry increases (a) persuadability (Bailenson & Yee, 2005), (b) the likelihood that people will follow recommendations (Jacob et al., 2011), (c) rapport and trust (Bernieri, 1988; for reviews, see Farley, 2014; Guéguen, 2009), (d) attraction (Chartrand & Bargh, 1999), (e) interdependent self-construals (van Baaren et al., 2003), and (f) the amount of personal information disclosed (Guéguen et al., 2012).

Moreover, as with most of the other domains, clinical textbooks emphasized the relevance of the quality of the clinician's voice in the therapeutic context. Clinical textbooks agreed that the quality of the clinician's voice, when spoken audibly and at a slow rate, was associated with acceptance and respect (Cormier et al., 2003), enhanced interest and empathy (Sommers-Flanagan & Sommers-Flanagan, 2015), warmth and interest (Ivey et al., 2010), and stronger rapport and comfort (Hill, 2009). Higher vocal frequency, similarly, has been linked to efforts to gain another person's acceptance. Vocal pleasantness is considered part of the expression of emotion (Scherer, 2003) and, relevant here, as an affiliation cue (Cappella, 1981; Farley et al., 2013; Hughes et al., 2010). For instance, people speak with a high-pitched voice when flirting (Puts et al., 2011) and when talking to infants or to the elderly (Bombar & Littig, 1996; Caporael, 1981).

Of the 18 coaching textbooks, seven spoke to the importance of using behavior when communicating with players. An average of 3.43 (SD = 1.27) behaviors were mentioned per textbook. The function of nonverbal behavior was proposed to (a) make the athlete feel accepted and important (Martens, 2012; Moore & Tschannen-Moran, 2010; Murphy, 2005; Weinberg & Gould, 2007), (b) facilitate active listening (Burton & Raedeke, 2008; J. M. Williams, 2010), and (c) enhance the coach's overall effectiveness (Moore & Tschannen-Moran, 2010; Murphy, 2005).

Compared with other disciplines, coaching textbooks included fewer citations and mentioned fewer different behaviors. One textbook based their description of the proscribed nonverbal behaviors on the SOLER method. The SOLER method states that the listener should square up and face the client, open their posture, lean toward the client, maintain eye contact, and relax one's posture (Egan, 2002). Among the behaviors most commonly mentioned by textbooks from other disciplines, only eye contact, physical contact, and body orientation was mentioned by three or more coaching textbooks, and those behaviors were each mentioned through the SOLER method.

Twelve of the 19 business textbooks included a description of how people in a business setting should act to build trusting relationships with coworkers. They mentioned an average of 6.08 (SD = 3.40) behaviors per textbook. The purpose of various behaviors is to engage in empathic listening (e.g., Bovée & Thill, 2008; Munter & Hamilton, 2012) and develop trust (e.g., Bovée & Thill, 2008; Reece, 2014). Business textbooks mentioned eye contact, nodding in agreement, smiling frequently, maintaining an appropriate physical distance, leaning forward, and sitting upright.

As with descriptions from other disciplines, empathic listening was presented as engaging in several nonverbal behaviors, including eye contact, leaning forward, smiling, nodding along with what the speaker says, and keeping an open posture (e.g., Kinicki & Fugate, 2016; Raman & Singh, 2012). As with the clinical context, there was an emphasis on the use of one's voice. Some textbooks proposed that the speaker's credibility was affected by their voice's tempo, tone, and pacing. Indeed, these changes to the quality of one's voice may affect views of authority and firmness (Raman & Singh, 2012) and varying tone keeps interest by emphasizing key points (Martel & Martel, 1989).

Of the 38 education textbooks, 13 made mention of nonverbal behaviors, and they mentioned an average of 3.85 (SD = 2.08) behaviors per textbook. The textbooks mentioned a similar set of behaviors compared with other disciplines, including eye contact, head nodding, smiling, laughter, and maintaining close proximity.

However, this discipline, compared with other disciplines, was split regarding the theoretical foundation for why it was important to engage in various affiliative displays. On the one hand, a large portion of the textbook authors emphasized the ability of affiliative behavior to produce a trusting and warm learning environment. Such behaviors thus communicate "liking and affect" (P. J. Cooper & Simonds, 2007) and help students feel comfortable and is key to unlocking the "authentic teacher" who is trustworthy and sincere (Henley, 2006). On the other hand, a minority of textbooks took a different theoretical approach, such that they focused on positive reinforcement as the reason for expressing affiliative behavior. From this perspective, their expression operates to reward students for engaging in desirable behavior, and its absence works to reduce undesirable behavior (e.g., Kellough et al., 2006).

With regards to specific behaviors, the education textbooks stressed the value of smiling. Although smiling was not mentioned at a rate different from chance, χ²(1) = 1.92, p = .16, the justifications of those who did recommend it conformed to other literatures. Wong and Wong (2018), for instance, noted that smiles communicate graciousness and hospitality, they also communicate understanding, peace, and harmony. The reasoning behind the recommendations for smiling was consistent with the broader research on the function that smiles play in interpersonal interactions. Smiles are detected, perceived, and used as a cue to develop trust (Cashdan, 1998; Fridlund, 1994; Godoy et al., 2005; Krumhuber et al., 2013; Mehu et al., 2007; Scharlemann et al., 2001). Other researchers have gone farther to propose that smiles are "costly signals," such that they increase trust while increasing the chance of being taken advantage of (Centorrino et al., 2011; Mehu & N’Diaye, 2010).

A noteworthy conclusion from the education textbooks was the recommendation regarding physical contact with students. On the one hand, the textbooks stressed the value that physical contact—a hand on the shoulder, a pat on the back, a touch on the arm—has on developing trust (Chesebro & McCroskey, 2002; P. J. Cooper & Simonds, 2007; Emmer & Evertson, 2013; Weinstein & Mignano, 2007). However, touch was not recommended at a rate different from chance, χ²(1) = 0.69, p = .40. For the textbooks that did recommend it, touch provides emotional support, tenderness, and encouragement. Touch is thus used to communicate caring and understanding (P. J. Cooper & Simonds, 2007) and as a form of reinforcement (Chesebro & McCroskey, 2002). Touch has been described as the most direct and immediate developer of trust (Thayer, 1986). This view of touch aligns with the broader literature's, such that physical contact is a powerful cue to develop trust and liking (Hornik, 1991, 1992; Hornik & Ellis, 1988; S. A. Rose, 1990; Whitcher & Fisher, 1979; for a review, see Gallace & Spence, 2010). Beyond the educational realm, other disciplines pointed to the role of physical touch. Future medical professionals were encouraged to initiate physical contact to convey empathy (e.g., Bickley et al., 2007; Roter & Hall, 2006), relax and provide comfort (e.g., Birrer, 1987), and reassure and express concern (e.g., Lipkin et al., 1995; Myerscough & Ford, 1996). For coaching, Anshel (2012) recommended that coaches use physical touch, most commonly as a pat on the back or an arm around the shoulders, to benefit their interactions with their athletes.

On the other hand, textbook authors acknowledged that changing cultural norms (e.g., the MeToo movement) and age-specific norms makes it problematic to make any physical contact despite its benefits (e.g., Sommers-Flanagan & Sommers-Flanagan, 2015). Teachers are often warned not to touch students and that the anxiety around touching tends to decline with teaching experience (Weinstein & Mignano, 2007), but Henley (2006) noted that touch can be comforting in appropriate situations, such as with an emotionally distraught 6-year-old (who had fallen or had a disagreement with a fellow student).

Of the 11 leadership textbooks, nine mentioned nonverbal behaviors, and they mentioned an average of 3.82 (SD = 1.33) behaviors per textbook. There was less of a consensus in this discipline, as only one behavior, eye contact, was mentioned by more than half of the sources. Indeed, eye contact was mentioned at a frequency unlikely to occur by chance, χ²(1) = 5.44, p = .02. Other behaviors mentioned by a third of textbooks included eye contact, head nodding, smiling, laughter, and maintaining close proximity.

The one point of consensus was eye contact, with textbook authors noting that it worked to communicate interest and intimacy (e.g., Hart, 2010; Polack & Avtgis, 2011), facilitate empathic engagement (Hojat, 2006), enhance the ability to read emotional cues and recognize distress (Roter & Hall, 2006), facilitate client's comfort (Birrer, 1987), and help with active listening (Polack & Avtgis, 2011; Roter & Hall, 2006).

As with law, there was a pattern whereby the function of affiliative behavior was described as relevant to communicate trust and expertise. Such behaviors—which were summarized by "SOFTEN," proscribed smiles, open stance, forward lean, tone, eye contact, and head nod—project both confidence and approachability (Cardon, 2018) and competence and trust (Gamble & Gamble, 2013; Hackman & Johnson, 2009). These behaviors were viewed as strengthening credibility by being seen as confident (Halpern & Lubar, 2004).

Behaviors mentioned in the attraction and parent-infant interaction literatures are presented in Table 2. Behaviors with clear empirical support were indicated with an X.

A secondary question focused on whether different behaviors were recommended in situations in which trust needed to be built quickly versus more slowly. One difference emerged in the tendency to recommend mimicry-like behaviors. The clinical textbooks recommended behaviors fitting into the category of mimicry (e.g., matching vocal tone, body position) more often than other disciplines. This could be due in part to the training that therapists receive. Indeed, mimicry is difficult to perform, and if done poorly or incorrectly, it could have negative consequences (Casasanto et al., 2020) or become less effective (Kulesza et al., 2016).

Another ancillary question focused on whether relative status (higher vs. equal) affected which affiliative behaviors were recommended. Two disciplines allowed for a specific comparison: business and leadership. One difference was the emphasis placed on sitting/standing behavior and body lean, which was recommended in the business textbooks, but not as often in leadership textbooks. One reason for this was thought to be the implied audiences. Leadership texts assumed the speaker was presenting to a group of employees whereas business texts focused more on one-on-one communication with peers and supervisors (e.g., Barrett, 2006; Cardon, 2018). However, the contrast between the behaviors for leadership and business revealed no differences between these areas.

An important question is the degree to which nonverbal behavior "matters" in the professional context. On the one hand, estimates of how much information is conveyed nonverbally indicates the answer to the question may be "quite a bit." For instance, Mehrabian and Ferris (1967) are reported as claiming that 93% of all information is communicated nonverbally. Similarly, Hall (1966) claimed that 90% of communication cues was "hidden cultural grammar," and other researchers propose similarly high estimates: Munter and Hamilton (2012) proposed 60–90%, Birdwhistell (1970) advocated for 65%, McElhaney (2005) proposed 60%, Ingram et al. (2012) proposed 50%, and Futrell (2008) and Quintanilla and Wahl (2014) both suggested 55%. On the other hand, the percentage of information that is convoyed nonverbally may be highly dependent on the context. Although the most often cited statistic is Mehrabian and colleague's 93%, Mehrabian (1995, as cited in Lapakko, 1997, p. 65) himself later stated that this question was difficult to answer, "My findings are often misquoted.... Clearly, it is absurd to imply or suggest that the verbal portion of all communication constitutes only 7% of the message. Suppose I want to tell you that the eraser you are looking for is in the second right-hand drawer of my desk in my third-floor office. How could anyone contend that the verbal part of this message is only 7% of the message?"

Whatever percentage nonverbal behavior plays, trust improves outcomes with clients. In the medical field, the absence of trust can take the form of failure to continue treatment (Hillen et al., 2011; Zolnierek & DiMatteo, 2009), reduced information sharing and closed off communication (Mechanic, 1998), greater patient fear (Hillen et al., 2011), and lowered patient satisfaction (Mowen et al., 1993; Ong et al., 1995; S. Williams et al., 1998). Similarly, in the therapeutic context, clients who do not trust their therapist are more opposed to the proposed treatment (Castonguay et al., 1996). Alternatively, in coaching, players who trust their coach report higher levels of satisfaction with the coaching (Kao et al., 2017) and demonstrate increases in performance, commitment, and cooperation (Zhang & Chelladurai, 2013). But when athletes mistrust their coach or perceive a breach in trust, they report a higher likelihood of leaving the team (Barnhill & Turner, 2013). In the marketplace, trust predicts the strength of a buyer-seller relationship (Ganesan, 1994) and the perceived continuity of a buyer-seller relationship (E. Anderson & Weitz, 1989).

Despite the disparate nature of the examined disciplines, an analysis of 86 textbooks across 8 disciplines arrived at a consistent set of recommendations for how to build interpersonal trust. A small subject of behaviors, including eye contact, mimicry, smiling, and maintaining physical proximity, were repeatedly recommended. Not only were the recommended behaviors consistent, but those behaviors were consistent with the behaviors used by parents and by people when they communicate liking. Although subtle differences persisted across disciplines—making domain-specific examination relevant—a core set of nonverbal behaviors remained important.