586570

research-article2015

JADXXX10.1177/1087054715586570Journal of Attention DisordersTran and Voracek

Article

Footedness Is Associated With ADHD Symptoms in the Adult General Population

Journal of Attention Disorders 1­–8 © 2015 SAGE Publications Reprints and permissions: sagepub.com/journalsPermissions.nav DOI: 10.1177/1087054715586570 jad.sagepub.com

Ulrich S. Tran1 and Martin Voracek1

Abstract Objective: Mixed-handedness among children has recently been proposed as a marker of neurodevelopmental disorder and ADHD. This study expanded this initial evidence to the questions of whether mixed-handedness as well as mixedfootedness are similarly associated with ADHD among adults. Method: Self-reported ADHD symptoms, handedness, footedness, and current depression and anxiety were assessed in a large, heterogeneous general population sample (N = 2,592). Latent variable analysis was used to investigate the structure and measurement properties of ADHD symptoms, the dimensionality of footedness, and the classification of lateral preferences. Results: Mixed-footedness was associated with probable ADHD (odds ratio [OR] = 1.76 [1.07, 2.89], p = .026). Left- and mixed-footedness were associated with higher inattention and impulsivity scores. Conclusion: Developmental continuities of the associations of mixed lateral preferences with ADHD from child to adult age seem to exist. In particular, mixed-footedness, rather than mixed-handedness, appears to be an ADHD marker among adults. (J. of Att. Dis. XXXX; XX(X) XX-XX) Keywords adult ADHD, handedness, footedness, general population, latent variable analysis

Introduction ADHD is a neurodevelopmental disorder, affecting about 5% of children according to Diagnostic and Statistical Manual of Mental Disorders (5th ed.; DSM-5; American Psychiatric Association [APA], 2013). For about two thirds of child-age patients, ADHD symptoms last into adulthood (Faraone, Biederman, & Mick, 2006). The prevalence of adult ADHD is around 2.5% (APA, 2013), with higher prevalence rates in higher income than in lower income countries (Fayyad et al., 2007). ADHD has an average heritability of around 76% (Faraone et al., 2005), but environmental factors, particularly prenatal risk factors, such as exposure to nicotine, alcohol, and drugs; maternal stress; preterm birth; and low birth weight, also play a role in the development of the disorder (Kooij et al., 2010). Furthermore, in two large Scandinavian birth cohort studies, mixed-handedness has been found to be associated with symptoms of ADHD among 5-year-olds (Rodriguez & Waldenström, 2008; N = 1,714) and among 8-year-olds (Rodriguez et al., 2010; N = 7,871). Mixed-handedness was further associated with the persistency of symptoms 8 years later, when the children were 16 years old. Handedness is considered as an indicator of brain hemispheric lateralization, with mixed- and left-handedness indicating a raised likelihood for atypical (i.e., non-left

brain hemispheric) language lateralization (Szaflarski et al., 2002). Brain dysfunctions, involving fronto-striatal and parietal cortical networks, and structural brain abnormalities are neural substrates of ADHD, both in children and adults (see Kooij et al., 2010, for an overview of studies). Specifically, abnormalities appear to affect predominantly the right brain hemisphere (Hart, Radua, Nakao, MataixCols, & Rubia, 2013). Besides being an indicator of atypical brain lateralization, mixed-handedness is associated with prenatal exposure to maternal distress (Glover, O’Connor, Heron, Golding, & The ALSPAC Study Team, 2004) and neurodevelopmental instability (Rodriguez & Waldenström, 2008), thus making it a candidate marker of neurodevelopmental problems and disorders, including ADHD (Rodriguez et al., 2010). Handedness is an easily accessible clinical marker whose associations with ADHD in children proved to be both meaningful and to hold over time; hence, it may be useful for the identification of persons at risk and may also enable new insights into possible causal factors of ADHD (Rodriguez et al., 2010). 1

University of Vienna, Austria

Corresponding Author: Ulrich S. Tran, Department of Basic Psychological Research and Research Methods, School of Psychology, University of Vienna, Liebiggasse 5, A-1010 Vienna, Austria. Email: [email protected]

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Journal of Attention Disorders 

Whereas mixed-handedness appears to be a relatively rare condition (1.1% of children were mixed-handed in Rodriguez et al., 2010, and 2%-7% of adults, according to Tran, Stieger, & Voracek, 2014a), mixed-footedness is much more common (26%-35% of adults in Tran et al., 2014a) and probably a more relevant indicator of neurodevelopmental disorder than mixed-handedness. In adults, mixed-footedness is indicative of a higher load of schizotypal traits (Tran, Stieger, & Voracek, 2015), for which neurodevelopmental instability is considered as one possible cause (Golembo-Smith et al., 2012). Also, among adults footedness has been shown to be a stronger indicator of language lateralization than handedness (e.g., Elias & Bryden, 1998). In conjoint analyses of common sidedness traits (handedness, footedness, earedness, and eyedness), footedness has emerged as the most relevant indicator of overall sidedness (Tran et al., 2014a). Previous studies on handedness and ADHD have been limited in their assessment of handedness, by using singleitem measures (Rodriguez et al., 2010) or arbitrary handedness classification criteria (Rodriguez & Waldenström, 2008), and have not examined adult populations or the associations of ADHD with footedness. Hence, the goal of the present study was to examine the associations of handedness and footedness with ADHD symptoms and probable ADHD in a large and heterogeneous general population sample of adults, using multi-item lateral preference inventories and reliable methods of lateral preference classification. Analysis also controlled for symptoms of depression and anxiety, known to be frequently co-occurring with ADHD (Kooij et al., 2010). There is some evidence that, unlike handedness, which is unidimensional (Tran et al., 2014a), footedness is two-dimensional, differentiating skilled versus unskilled/movement tasks (e.g., Kalaycıoğlu, Kara, Atbaşoğlu, & Nalçacı, 2008). Therefore, we also examined the dimensionality of footedness. We expected that mixed lateral preferences would predict ADHD symptoms among adults as well, but that mixed-footedness would emerge as a stronger predictor than mixed-handedness. To date, measurement equivalence of self-report adult ADHD scales with regard to respondent sex has not been examined, despite the fact that the prevalence of ADHD is higher among men than women (around 1.5:1; Fayyad et al., 2007). Furthermore, the factorial validity of adult ADHD symptoms currently is unclear. In the DSM-5 (as well as in the older Diagnostic and Statistical Manual of Mental Disorders [4th ed.; DSM-IV; APA, 1994]) conceptualization, symptoms are evaluated on two dimensions, namely inattention and combined hyperactivity–impulsivity (e.g., Kessler, Adler, Ames, et al., 2005). In the International Classification of Diseases (ICD-10; World Health Organization [WHO], 1992) conceptualization, symptoms are evaluated on three dimensions, thereby additionally differentiating hyperactivity from impulsivity (e.g.,

Rösler et al., 2004). Previous research has indicated that three factors may provide a better fit to empirical data than two factors; however, items also tend to cross-load on other than their designated factors (see McKee, 2012, for original data and an overview of studies). A second goal of the present study was therefore to examine the structural and measurement properties of self-reported ADHD symptoms, utilizing state-of-the-art structural equation modeling techniques.

Method Participants The sample comprised 2,592 participants (53.8% women) from the general population, covering the full adult age range (18-93 years; M = 35.29 years, SD = 15.47; interquartile range = 23-48 years). The majority of the participants were Austrian (61.1%) or German (29.8%; other nationalities = 9.0%).

Materials Symptoms of ADHD were assessed with the ADHD SelfRating scale (ADHD-SR; Rösler et al., 2004), which evaluates the prevalence and severity of 18 symptoms of inattention, hyperactivity, and impulsivity according to the DSM-IV on 4-point scales, ranging from 0 = not at all to 3 = severe. The ADHD-SR allows calculating a total score (all 18 items combined) as well as three subscale scores, following the ICD-10 conceptualization, namely, for inattention (9 items), hyperactivity (5 items), and impulsivity (4 items). The impulsivity subscale includes 4, rather than 3, items, as “talks excessively” is considered to be a symptom of impulsivity in the ICD-10, rather than one of hyperactivity as in the DSM-IV (and DSM-5). Cronbach’s alpha in the current sample was .83 for total scores, and for subscale scores .75 (inattention), .73 (hyperactivity), and .71 (impulsivity). The ADHD-SR is well-validated and widely used in research (for a recent example, see Roy et al., 2015). Previous studies (Rösler et al., 2004) have shown good agreement of self-report scale scores with expert ratings. For the classification of adult ADHD, Rösler et al. (2004) recommended a cutoff of ≥15, which yields a 77% sensitivity and 75% specificity for diagnosis. This cutoff was also used in the present study. However, to conform better to diagnostic criteria, classification of probable ADHD further required that symptoms were distinctively present already during school years (ADHD-SR Item 19; scoring 3 = severe). Handedness was assessed with a 10-item scale validated by Tran et al. (2014a). The scale comprised the 10 psychometrically most reliable and informative handedness items from the Lateral Preference Inventory (LPI; Coren, 1993)

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Tran and Voracek and the Edinburgh Handedness Inventory (Oldfield, 1971). Response options were always right, usually right, no preference, usually left, and always left (in this order), coded +2, +1, 0, −1, and −2, respectively. Following psychometrically based recommendations (Tran et al., 2014a), the response options always and usually were combined for analysis. Cronbach’s alpha of the handedness composite was .97 in the current sample. Footedness was assessed with nine items: the four items of the LPI footedness scale (foot preference for kicking a ball to hit a target; picking up a pebble with the toes; stepping on a beetle or a cigarette stump; stepping up onto a chair) and five items from Kalaycıoğlu et al. (2008). The four-item LPI footedness scale has previously been validated by Tran et al. (2014a). Items from Kalaycıoğlu et al. (2008) were selected for their trait coverage with regard to those bipedal movement tasks (first foot when stepping forward; when stepping up stairs; when stepping up stairs backwards) that load highest on a factor of foot movement tasks, and with regard to those unipedal skilled tasks (tracing a letter while standing; erasing that letter) that load highest on a factor of skilled foot tasks. Footedness items were scored like the handedness items. Cronbach’s alpha of the nine-item footedness scale was .89 in the current sample. Current symptoms of depression and anxiety were assessed with the respective scales of the Brief Symptom Inventory (German form; Franke, 2000). Six items each assessed the prevalence and symptom distress during the past 7 days, scored on 5-point scales from 0 = not at all to 4 = extremely. Cronbach’s alpha was .84 (depression) and .77 (anxiety) in the current sample.

Procedure Data were collected in the course of a larger project on individual difference variables by a multitude of independent data collectors. Participants had to be fluent in the survey language German and were approached on a personal basis, using word of mouth and personal contacts. Apart from insufficient language proficiency, there were no exclusion criteria. Study participation was voluntary, anonymous, and participants were not remunerated for participation.

Analysis Dimensionality and measurement invariance of the ADHD-SR were investigated with multigroup confirmatory factor analysis (CFA) and exploratory structural equation modeling (ESEM; Asparouhov & Muthén, 2009). ESEM allows for a flexible examination of factor structures, as it integrates exploratory and confirmatory approaches. Crossloadings are freely estimated in ESEM, as is customary in the exploratory factor analysis framework. Standard errors

and goodness-of-fit statistics are provided, as in conventional SEM and CFA. We fitted a three-factor CFA model to the data, testing the fit of the scale structure proposed by Rösler et al. (2004). Expecting problems in model fit, we also investigated the fit of three- and four-factor ESEM models, utilizing the weighted least square mean- and variance-adjusted (WLSMV) estimator of Mplus 6.11 (Muthén & Muthén, 2008). The WLSMV estimator is based on the polychoric item correlation matrix, thus conforming to the ordered-categorical item response format. Analyses tested for full measurement invariance between men and women, constraining factor loadings and item thresholds to equality between groups. Factor means and variances were set to 0 and 1 among women in these analyses, thereby estimating these parameters freely among men. Model fit was evaluated with the comparative fit index (CFI), the Tucker–Lewis index (TLI), and the root mean square error of approximation (RMSEA), using the benchmarks of Hu and Bentler (1999)—CFI/TLI: good fit ≥.95, acceptable fit ≥.90; RMSEA: good fit