Sex differences in ADHD: Conference summary

Clinical samples of attention deficit hyperactivity disorder (ADHD) have been dominated by males. Consequently, female manifestations and sex differences have been relatively neglected in the extensive ADHD research. Because ADHD is so common (3% to 5% of school children) and chronic (lifelong in many cases), even a small proportion of females multiplied by such a large base means hundreds of thousands of girls and women with ADHD, a significant public health problem. An NIMH conference concluded that research is needed not only on sex differences related to ADHD, but also on manifestations of ADHD in females as such. Areas of focus should include differences in life course (sex-differential age effects); effects of hormones; effects of ADHD parenting (in utero and postnatal) on the next generation; response to and implications for design of psychosocial treatment; effects of differential comorbidity; normative background sex differences that influence the manifestation of ADHD; differences in development of verbal fluency and social behavior; possible interactions of sex and ethnicity; a prospective study of both sex offspring of ADHD adults; and such methodological issues as appropriate instruments and diagnostic thresholds, power to prevent false negatives, valid impairment measures, validity and reliability of child self-reports, and more inclusive samples (all three subtypes: inattentive, hyperactive-impulsive, and combined).The following participants in the November 16–17, 1994, NIMH Conference on Sex Differences in ADHD may be considered ghost co-authors of the contents in this summary. Special thanks are due to Euthymia Hibbs, Ph.D., co-organizer of the conference; Peter Jensen, M.D., who suggested the successful format; Delores Parron, Ph.D., who gave much helpful advice on the conference arrangements; Emily Areia, Ph.D., who thoroughly critiqued the summary; Joan Cole, who helped abstract the recorded proceedings; and Jose Bauermeister, Ph. D., F. Xavier Castellanos, M.D., Stephen Hinshaw, Ph.D., and Mark Stein, Ph.D., who helped with referencing. Other participants, in alphabetical order, included Russell Barkley, Ph.D.; Joseph Biederman, M.D.; Caryn Carlson, Ph.D.; C. Keith Conners, Ph.D.; Monique Ernst, M.D.; Miranda Gaub; Jay N. Giedd, M.D.; Michael Gordon, Ph.D.; Jeffrey Halperin, Ph. D.; Betsy Hoza, Ph.D.; Hans Huessy, M.D.; Jean King, Ph.D.; Kathleen Kiely; Rachel Klein, Ph.D.; Benjamin Lahey, Ph.D.; Jan Loney, Ph.D.; Elizabeth Lorch, Ph.D.; Spero Manson, Ph.D.; Keith McBurnett, Ph.D.; Richard Milich, Ph.D.; Douglas Novins, M.D.; Daisy Pascualvaca, Ph.D.; Linda Pfiffner, Ph.D.; Jane Steinberg, Ph.D.; James Swanson, Ph.D.; Marcus Thomeer, Ph.D.; Lillie Williams, M.D.; Alan Zametkin, M.D.The opinions expressed herein are the views of the author and conference participants and do not necessarily reflect the official position of the National Institute of Mental Health or any other part of the U.S. Department of Health and Human Services.     

Sex differences in ADHD trajectories across childhood and adolescence

Previous studies have hinted at sex differences in developmental trajectories in ADHD symptoms; however, little is known about the nature or cause of these differences and their implications for clinical practice. We used growth mixture modelling in a community‐ascertained cohort of n = 1,571 participants to study sex differences in ADHD symptom developmental trajectories across the elementary and secondary school years. Participants were measured at ages 7, 8, 9, 10, 11, 12, 13, and 15. We found that females were more likely to show large symptom increases in early adolescence while males were more likely to show elevated symptoms from childhood. For both males and females, early adolescence represented a period of vulnerability characterized by relatively sudden symptom increases. Females affected by hyperactivity/impulsivity may be more likely to be excluded from diagnosis due to current age of onset criteria. More attention should be paid to early adolescence as a period of risk for hyperactivity/impulsivity symptom onset or worsening.     

Intellectual functioning in adults with ADHD: a meta-analytic examination of full scale IQ differences between adults with and without ADHD

Although attention has been given to the intellectual functioning of children with attention-deficit/hyperactivity disorder (ADHD) relative to their non-ADHD peers, few studies have examined intellectual functioning in adults with ADHD. The purpose of the current investigation was to examine differences in intellectual ability between adults with and without ADHD via a meta-analytic review. Of the 33 studies meeting inclusion criteria, primary analyses focused on 18 studies representing 1,031 adults with ADHD and 928 non-ADHD, nonclinical comparison adults and containing Wechsler Adult Intelligence Scale (WAIS; D. Wechsler, 1955, 1981, 1994) Full Scale IQ scores or estimates. A significant effect was found such that adults with ADHD scored lower than non-ADHD adults on WAIS intelligence tests. However, this difference was small and not clinically meaningful. The presence of several moderators reflecting characteristics of the ADHD samples and study methodology suggested that only a subset of adults with ADHD (e.g., those with comorbid disorders) may experience lower general intellectual ability relative to non-ADHD comparison adults. Implications of the findings for clinical and research settings are presented as well as suggestions for improving methodology and reporting in future research.     

Sex and ear differences in spontaneous and click-evoked otoacoustic emissions in young adults

Effects of sex and handedness on the production of spontaneous and click-evoked otoacoustic emissions (OAEs) were explored in a non-hearing impaired population (ages 17-25 years). A sex difference in OAEs, either produced spontaneously (spontaneous OAEs or SOAEs) or in response to auditory stimuli (click-evoked OAEs or CEOAEs) has been reported in infants and children, but healthy young adults seldom have been the target of study. In the current data, a robust sexual dimorphism was confirmed, with women producing more numerous and stronger SOAEs, and CEOAEs with greater response amplitude compared to men. A right-ear advantage was found for the number of SOAEs produced and, in women, for SOAE power. Although handedness did not moderate the ear asymmetry in production, exploratory analyses revealed that departures from strong right hand preference were associated in the present sample with reduced numbers or strengths of OAEs. The results are discussed with respect to differential exposure to androgens during prenatal development.     

Sex differences in cognition

Sex differences in cognitive skills, grouped into three areas — motor, spatial, and linguistic — are assessed in the context of current notions of cerebral lateralization (Buffery and Gray, 1972). There are few convincing sex differences, either overall, or in interactions with (putative) functional localization. There are several qualifying criteria (nature of further interactions with age, birth order, culture, sex of experimenter, sex role pressure) which would have to be met, but these are as yet inadequately documented. Serious caution is urged on the proliferating number of researchers in this area.     

Sex differences in depression

The role of housewife has been hypothesized as the source of excess mental illness among married women as compared with married men. The present study found both housewives and working wives significantly more depressed than working husbands. Although working wives report that they do more housework than husbands, this factor was not significantly related to depression for either wives or husbands. It is suggested that the risk factors for depression, including marriage for women, may be better understood in the context of clinical theories of depression, especially the learned helplessness model.     

Sex differences in pain

Are there sex differences in pain? For experimentally delivered somatic stimuli, females have lower thresholds, greater ability to discriminate, higher pain ratings, and less tolerance of noxious stimuli than males. These differences, however, are small, exist only for certain forms of stimulation and are affected by many situational variables such as presence of disease, experimental setting, and even nutritive status. For endogenous pains, women report more multiple pains in more body regions than men. With no obvious underlying rationale, some painful diseases are more prevalent among females, others among males and, for many diseases, symptoms differ between females and males. Sex differences in attitudes exist that affect not only reporting, coping, and responses to treatment, but also measurement and treatment. So many variables are operative, however, that the most striking feature of sex differences in reported pain experience is the apparent overall lack of them. On the other hand, deduction from known biological sex differences suggests that these are powerful sex differences in the operation of pain mechanisms. First, the vaginal canal provides an additional route in women for internal trauma and invasion by pathological agents that puts them at greater risk for developing hyperalgesia in multiple body regions. Second, sex differences in temporal patterns are likely to give rise to sex differences in how pain is "learned" and stimuli are interpreted, a situation that could lead to a greater variability and wider range of pains without obvious peripheral pathology among females. Third, sex differences in the actions of sex hormones suggest pain-relevant differences in the operation of many neuroactive agents, opiate and nonopiate systems, nerve growth factor, and the sympathetic system. Thus, while inductive analysis of existing data demonstrate more similarities than differences in pain experience between females and males, deductive analysis suggests important operational sex differences in its production.     

Sex differences in self-silencing

The construct of self-silencing was proposed to account for women's greater vulnerability to developing depression. This study of 1,117 students (795 women and 322 men) explored possible explanations for the empirical finding that men self-silence to the same or greater extent than women. Analysis showed that men reported more self-silencing than women. A factor analysis confirmed the subscale structure of the Silencing the Self Scale for women and men, with relatively few departures from the originally proposed subscales. Depression and self-silencing scores were correlated positively for both men and women. The results of two multiple regressions, performed separately for men and women, showed that depressive symptomatology accounted for a significant percentage of the variance in self-silencing but that social desirability did not account for a significant increment in the variance accounted for in silencing the self. The scores on the Care as Self-sacrifice and the Divided Self subscales were intercorrelated for women, but not for men, indicating that there may be a sex difference in perception of self-silencing behavior.     

Sex differences in the adolescent brain

Adolescence is a time of increased divergence between males and females in physical characteristics, behavior, and risk for psychopathology. Here we will review data regarding sex differences in brain structure and function during this period of the lifespan. The most consistent sex difference in brain morphometry is the 9–12% larger brain size that has been reported in males. Individual brain regions that have most consistently been reported as different in males and females include the basal ganglia, hippocampus, and amygdala. Diffusion tensor imaging and magnetization transfer imaging studies have also shown sex differences in white matter development during adolescence. Functional imaging studies have shown different patterns of activation without differences in performance, suggesting male and female brains may use slightly different strategies for achieving similar cognitive abilities. Longitudinal studies have shown sex differences in the trajectory of brain development, with females reaching peak values of brain volumes earlier than males. Although compelling, these sex differences are present as group averages and should not be taken as indicative of relative capacities of males or females.     

Sex differences in the perception of touching

Sex differences in the perception of touching were investigated by having 25 male and 25 female college students rate how likeable a touch would be under different conditions. The women produced a more favorable affect than the men when they touched, and women were perceived as liking to be touched more than men. Perception of touching in general was correlated positively with Self-esteem for men, negatively with Machiavellianism for women, and positively with Trust for women. Results were discussed in terms of traditional sex-typing of touching behavior.     

Sex differences in the processing of flankers

The study of sex differences in cognition has often focused on differences in spatial processing. Recently, sex differences in selective attention have been observed by Bayliss, di Pellegrino, and Tipper (2005), showing that women are more influenced than men by irrelevant spatial cues. The current study elaborates on this finding and tests whether sex differences in the processing of irrelevant information also occur in a simpler task, in which there is no need to redirect visual attention and no need to remember multiple spatial stimulus–response associations. Here, attention is studied using a novel combination of a go/no-go task and a flanker task. A total of 80 neurotypical participants were studied, and it was found that responses in women were more strongly affected by flanker information than were responses in men. This suggests that these sex differences were not due to difficulties with spatial reorientation, or remembering spatial stimulus–response relationships. The findings are discussed in the context of the hunter–gatherer theory of sex differences.     

Sex differences in the generalization of attraction

The effects of intergroup evaluations on intragroup attraction were assessed in a situation involving two-person teams that were all of the same sex. Male (N=123) and female (N=118) group members separately reported their political views to another dyad and then received either unfavorable, favorable, or no feedback regarding their team as a whole on the basis of this information. The results indicated that females evidenced more anger in response to the out-group's unfavorable feedback than did males. These anger responses were related to attraction to ward a teammate for males but not for females. Moreover, males evidenced less attraction toward an in-group member after receiving unfavorable rather than favorable intergroup evaluations, whereas females did not. On the other hand, only for females was attraction to ward a teammate related to the perceived similarity of that individual within experimental conditions. Apparently, the greater cognitive orientation of females as compared to males to ward another ingroup member resulted in their being less susceptable to the influence of situationally induced affect.This research was performed as part of the author's doctoral dissertation submitted to the Department of Psychology, Purdue University. Portions of this paper were presented at the meeting of the Eastern Psychological Association held in Boston, 1977.It should be noted that the views expressed in this paper are those of the author and do not reflect those of the Army or any other government agency.