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Previous research has not explored the Five Factor Model of personality among adults who stutter. Therefore, the present study investigated the five personality domains of Neuroticism, Extraversion, Openness, Agreeableness and Conscientiousness, as measured by the NEO Five Factor Inventory (NEO-FFI), in a sample of 93 adults seeking speech treatment for stuttering, and compared these scores with normative data from an Australian and a United States sample. Results revealed that NEO-FFI scores for the stuttering group were within the ‘average’ range for all five personality domains. However, adults who stutter were characterized by significantly higher Neuroticism, and significantly lower Agreeableness and Conscientiousness, than normative samples. No significant differences were found between groups on the dimensions of Extraversion and Openness. These results are discussed with reference to the relationship between personality factors among adults who stutter, their directionality, and implications for predicting treatment outcome. Learning outcomes: The reader will be able to: (1) describe the Five Factor Model of personality, including the NEO-FFI personality domains of Extraversion, Neuroticism, Openness, Agreeableness, and Conscientiousness, and (2) discuss differences in NEO-FFI domain scores between adults who stutter and normative samples, and (3) understand the clinical implications of personality profiles in terms of treatment process and outcome for adults who stutter.

Personality structure refers to “enduring emotional, interpersonal, experiential, attitudinal, and motivational styles” (McCrae, 1991, p. 399) which are fundamental to all individuals. Although personality is not considered to be a causal factor in the development of stuttering (Bloodstein and Bernstein Ratner, 2008 and Sermas and Cox, 1982), it has been suggested that the negative consequences of the disorder may have an adverse impact upon personality adjustment (Prins, 1972), quality of life, occupational success and overall functioning (Ruben, 2000 and Yaruss, 2001). Consequently, the personality structure of adults who stutter has been widely explored and debated (Sermas and Cox, 1982 and Van Riper, 1982). Past research has largely compared the personality profiles of adults who stutter with adults who do not stutter and psychiatric samples (Bloodstein and Bernstein Ratner, 2008, Goodstein, 1958 and Prins, 1972), and this focus has generated substantial controversy (Seery, Watkins, Mangelsdorf, & Shigeto, 2007). On the whole, research findings have not consistently or conclusively reported the presence of distinct personality traits in those who stutter or the presence of significant personality differences between stuttering and fluent populations (Andrews et al., 1983, Sermas and Cox, 1982 and Treon et al., 2006). For instance, a number of studies have reported heightened levels of neuroticism and introversion in adults who stutter (Bharath and Pranesha, 1970, Hegde, 1972 and Ying et al., 2003), whilst others have suggested that adults who stutter are no more neurotic or maladjusted than fluent adults (Andrews et al., 1983 and Bloch and Goodstein, 1971). Failure to find conclusive evidence of a distinct personality profile among adults who stutter has generally occurred regardless of the measures used to evaluate personality (Bloodstein and Bernstein Ratner, 2008, Goodstein, 1958 and Sermas and Cox, 1982). In particular, the Minnesota Multiphasic Personality Inventory (MMPI) (Hathaway & McKinley, 1967) has been employed in numerous studies, often with ambiguous results (Lanyon, 1966 and Ying et al., 2003). For instance, Sermas and Cox (1982) reported no significant differences in MMPI scores for a sample of stuttering individuals when compared with two groups of psychiatric patients. Treon et al. (2006), on the other hand, found that overall scores on the MMPI-2/A (Butcher et al., 1989 and Butcher et al., 1992) were significantly higher on overall tendency towards psychopathology in adolescents and adults who stutter when compared with matched controls. Less recent MMPI studies have indicated that higher levels of neuroticism and other personality facets often found in adults who stutter may not actually exceed normal limits (Dahlstrom and Craven, 1952 and Walnut, 1954). The Eysenck Personality Inventory (EPI) (Eysenck & Eysenck, 1964) has also been used to assess personality in stuttering samples (Bharath and Pranesha, 1970, McDonough and Quesal, 1988 and Ying et al., 2003). For instance, Hegde (1972) administered the EPI to a large sample of adults who stutter, and compared their scores with normative scores for psychiatric and normal individuals. The stuttering group demonstrated high introversion scores which were similar to, though slightly less than, a sample of anxiety patients. In addition, although neuroticism scores for the stuttering group fell within normal limits, over half of the sample was categorized as ‘neurotic’, with scores exceeding those of the general population. Guitar (1976) also administered the EPI to two groups of adults seeking treatment for stuttering, and found that increased neuroticism was associated with more negative attitudes about stuttering. Overall, ambiguity regarding the link between stuttering and personality (Prins, 1972) may be attributed to the different types of measures used to assess personality. Goodstein (1958), in particular, has highlighted the difficulties inherent in making generalizations about the personality profiles of adults who stutter due to the lack of standardized personality inventories used in past research. Furthermore, even when standardized personality inventories are used, different measures vary in terms of the characteristics they are designed to assess. For instance, the MMPI is typically used as a clinical measure of psychopathology and personality adjustment (Sermas & Cox, 1982), whereas the EPI measures the personality dimensions of Extraversion, Neuroticism and Psychoticism. Although these measures assess similar factors, they do not directly overlap (Curtin et al., 1995 and Montag and Comrey, 1982). More recently, Susca (2006) has suggested that the full-length NEO Personality Inventory-Revised (NEO PI-R) and the shortened-version NEO Five Factor Inventory (NEO-FFI) (Costa & McCrae, 1992b) may hold promise in exploring whether personality differences exist between adults who stutter and adults who do not stutter. Both the NEO PI-R and the NEO-FFI were developed as measures of the Five Factor Model of Personality (FFM) (Digman, 1990), which is a dominant model of personality in the field of psychology (Laverdiere et al., 2007). The FFM theorizes that individual differences in emotional, interpersonal and motivational styles can be summarized by the five basic personality factors of Neuroticism, Extraversion, Openness, Agreeableness, and Conscientiousness. According to this model (see Costa and McCrae, 1992b and McCrae, 1991), Neuroticism is characterized by susceptibility to psychological distress and the experience of negative emotions such as fear, sadness, anger, and embarrassment. Individuals scoring low on Neuroticism are generally calm, unemotional and hardy, whereas individuals scoring high on Neuroticism have a tendency towards self-consciousness, emotionality and vulnerability. Secondly, the personality dimension of Extraversion refers to an individual's propensity to demonstrate qualities of extraversion and/or introversion. Individuals scoring low on Extraversion tend to be introverted, reserved and independent, whereas individuals scoring high on Extraversion are typically sociable, talkative, and energetic. Thirdly, Openness relates to such qualities as imagination, creativity, and attentiveness to inner feelings. Individuals scoring low on Openness are generally considered to be conventional, conservative and uncurious, whereas individuals high on Openness tend to be curious about their inner and outer worlds, with a willingness to entertain novel and unconventional ideas. Fourthly, Agreeableness relates to interpersonal tendencies and behaviour. Individuals scoring low on Agreeableness are considered to be disagreeable, antagonistic and irritable, whereas individuals scoring high on Agreeableness are typically good-natured, cooperative, helpful, and altruistic. Finally, Conscientiousness relates to the control of impulses and the active process of planning, organization and performance of tasks. Individuals scoring low on Conscientiousness are generally characterized as disorganized, lazy and relaxed about goal achievement, whereas high Conscientiousness is associated with determination, organization, reliability and perseverance. It has been suggested that these five personality dimensions are fundamental to all adults (McCrae, 1991), and that personality structure can impact health and psychological outcomes (Bolger and Zuckerman, 1995 and Hampson et al., 2007). For this reason, it would be of value to evaluate these dimensions among adults who stutter, especially as the FFM has not previously been explored among adults who stutter. It is possible that adults who stutter may demonstrate high Neuroticism and low Extraversion. Neuroticism, in particular, is associated with susceptibility to psychological distress and the tendency to experience negative emotions, and is strongly linked with anxiety sensitivity and maladjustment (Cox et al., 1999 and McCrae, 1991), whereas low Extraversion is largely related to shyness and introversion (Costa & McCrae, 1992b). These personality dimensions may be relevant to adults who stutter when considering the psychological, emotional and social consequences that often result from a lifetime of communication difficulties (Blomgren et al., 2005, Cook and Fry, 2006, Craig, 2000, Craig, 2003 and Ginsberg, 2000). For instance, adults who stutter often encounter negative listener reactions (Turnbaugh, Guitar, & Hoffman, 1979), and are frequently the focus of negative stereotypes and stigma (Cook and Fry, 2006, Mackinnon et al., 2007 and Turnbaugh et al., 1979), including the common perception that they are anxious, self-conscious, tense, insecure and introverted (Dorsey and Guenther, 2000, Healey et al., 2007, Miller and Watson, 1992 and Snyder, 2001). The experience of stuttering has also been associated with lowered quality of life and feelings of shame, helplessness, fear and avoidance (Corcoran and Stewart, 1998, Plexico et al., 2005 and Yaruss, 2001). In addition to these negative consequences, stuttering is frequently associated with heightened levels of anxiety (Craig and Tran, 2006 and Menzies et al., 1999), and there is also mounting evidence of a high rate of social phobia among adults who stutter (Iverach et al., 2009b, Menzies et al., 2008, Schneier et al., 1997 and Stein et al., 1996). For instance, Iverach, O’Brian, et al. (2009) investigated the presence of anxiety disorders among 92 of the 93 adults seeking speech treatment for stuttering from the present study. When compared to matched controls from a national population sample, adults seeking treatment for stuttering demonstrated significantly increased odds of meeting criteria for any anxiety disorder, including social phobia, generalized anxiety disorder, and panic disorder. In particular, the stuttering group were found to demonstrate 16-fold to 34-fold increased odds of meeting criteria for a diagnosis of social phobia in the previous 12 months when compared to controls. Based on these findings, it is possible that some adults who stutter may also be characterized by distinct personality profiles on the dimensions of Neuroticism and Extraversion. This is particularly pertinent given that both high Neuroticism and low Extraversion have been associated with anxiety and depressive disorders, including social phobia (Bienvenu et al., 2001, Bienvenu et al., 2004 and Naragon-Gainey et al., 2009). Although previous research in the field of stuttering has highlighted the potential value of exploring Neuroticism and Extraversion among adults who stutter, little if anything is known about the personality dimensions of Openness, Agreeableness and Conscientiousness. Research regarding these dimensions may enhance our understanding of the personality structure of adults who stutter. Therefore, the present study aims to: (1) explore the Five Factor Model of personality among adults seeking speech treatment for stuttering on the five personality domains of Neuroticism, Extraversion, Openness, Agreeableness and Conscientiousness, as measured by the NEO Five Factor Inventory (NEO-FFI) (Costa & McCrae, 1992b), which is a shortened version of the NEO PI-R and to (2) compare scores on the five NEO-FFI personality domains for adults who stutter with normative data from an Australian and a United States sample. Based on previous research findings, and in light of the increased rate of anxiety and social phobia found in this same sample of adults seeking speech treatment for stuttering (Iverach, O’Brian, et al., 2009), it is hypothesized that adults who stutter will demonstrate: (1) higher scores on the dimension of Neuroticism and (2) lower scores on the dimension of Extraversion, when compared with normative samples.