Introduction

Attention deficit hyperactivity disorder (ADHD) is themost frequently encountered childhood-onset neuro-developmental disorder in the western world with aprevalence ranging from 5 to 10% in school agedchildren [9, 19]. ADHD is a clinically heterogeneousdisorder that exacts an enormous burden on societyin terms of financial cost, stress to families, andadverse academic and vocational outcomes [4]. Thedifferences in the number of children diagnosed and

treated across countries led to the argument thatADHD may be a value-laden social label, rather than alegitimate medical condition [7, 21]. The vast majorityof the investigations on ADHD were generated inNorth America and some western European coun-tries.

Recently, the diagnosis of ADHD has been recog-nised in different countries and cultures [9]. It is nowargued that the differing rates of ADHD betweendifferent countries in literature may reflect differentdiagnostic criteria, age range assessed, information

Abiodun O. AdewuyaOluwole O. Famuyiwa

Attention deficit hyperactivity disorderamong Nigerian primary school childrenPrevalence and co-morbid conditions

Accepted: 23 June 2006Published online: 28 November 2006

j Abstract Objective This studyaimed to determine the prevalenceof ADHD and co-morbid condi-tions in a sample of primaryschool children aged 7–12 years inNigeria. Method A two-stagedprocedure in which primaryschool pupils aged 6–12 years(n = 1112) were assessed forDSM-IV criteria of attentiondeficit hyperactivity disorder(ADHD) by their teachers in thefirst stage and their parents in thesecond stage. A flexible criterionwas used for estimating theprevalence. Results The preva-lence of ADHD was 8.7%. Theprevalence of the subtypes were:predominantly Inattentive 4.9%,predominantly hyperactive/impul-sive 1.2% and combined 2.6%. Themale to female ratio was 2:1 for allthe subtypes of ADHD excepthyperactive/impulsive which was3.2:1. The co-morbid conditions

include oppositional defiant dis-order (ODD – 25.8%), conductdisorder (CD – 9.3%) and anxiety/depression (20.6%). While ODDand CD were associated with thehyperactive/impulsive subtype,anxiety/depression was associatedwith inattentive subtype. Conclu-sion Our findings support thenotion that ADHD occurs acrosscultures. Given the prevalent rate,efforts should be made to map outstrategies for early identificationand referral of these children forproper evaluation and treatment.This study can serve as a platformfor future analytical studies aboutthis challenging research issue insub-Saharan Africa.

j Key words Attention deficithyperactivity disorder –cross cultural – prevalence –co-morbidity – Nigeria

ORIGINAL CONTRIBUTIONEur Child Adolesc Psychiatry (2007)16:10–15 DOI 10.1007/s00787-006-0569-9

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Dr. A.O. Adewuya, MBChB (&)O.O. Famuyiwa, FWACPDept. of Mental HealthObafemi Awolowo University TeachingHospitals ComplexWesley Guild HospitalILESA 233001, Osun state, NigeriaTel.: +234-805/561-7605E-Mail: biodunwuya@yahoo.com

O.O. Famuyiwa, FWACPDept. of PsychiatryCollege of MedicineUniversity of LagosLagos, Nigeria

sources, origin of samples, and impairment definition[9, 18].

The DSM-IV criteria define three subtypes ofADHD; inattentive, hyperactive/impulsive, and com-bined. Symptoms of ADHD should be present in twoor more settings (e.g. at home or in school). Thesymptoms must adversely affect functioning in schoolor in a social situation. Children who meet the diag-nostic criteria for the behavioural symptoms but whodemonstrate no functional impairment do not meetthe diagnostic criteria for ADHD [1]. The AmericanAcademy of Paediatrics recommended that the diag-nosis require information from both the parent andclassroom teacher regarding core symptoms ofADHD, duration of symptoms, degree of functionalimpairment and coexisting conditions [16].

While the prevalence of ADHD ranged from 5 to10% in the western world, a rate of 15.2% had beenfound in Israel [5], 15.8% in Columbia [6] and 8.1% inTurkey [8]. The subtypes of ADHD had also differedamong cultures. While the inattentive subtype was themost prevalent in US [20], Australia [10, 11] andIsrael [5], the combined subtype was the most fre-quent in Brazil [17] and Columbia [6] and thehyperactive/impulsivity subtype the most common inTurkey [8]. While most studies had found a prepon-derance of males, no gender difference was found inIsrael [5]. Studies however, agreed that oppositionaldefiant disorder (ODD), conduct disorder (CD) andanxiety/depression are highly co-morbid with ADHD.

Despite the large volume of research dedicated toADHD worldwide, the epidemiology of ADHD in subSaharan Africa is yet unknown. Searches of literature,both electronic and manual revealed only few studiesdone on ADHD in this region. The available studiesdone in Ethiopia [2, 3] have found a prevalence of1.5% among pupils, with children between 10 and14 years of age having more than three-fold increasedrisk of ADHD compared with younger children. Thesestudies are few and are based on parents’ interviewalone whereas the diagnosis of ADHD is supposed tobe based on both parent and teacher’s reports. Withthe significant effects on children’s functioning acrossmultiple areas [14], and since individuals presentingwith ADHD in childhood may continue to showsymptoms as they enter adolescence and adult life,early detection is necessary to help direct individu-alized management to improve the psychosocial andeducational development of children with ADHD.

This study aimed to determine the prevalence ofADHD and co-occurring conditions in a Nigeriansample of primary school children aged 7–12 years.Since prevalence rates of ADHD vary widely,depending on the population assessed and themethodology used, we adopted a method similar tothat used in the Multimodal study of ADHD [15]. This

flexible criterion requires at least six behaviours ineither dimension by either parent or teacher with theother individual reporting at least three behaviours ineither dimension. Both the teacher and parent mustreport impairment.

Methods

j Participants

The study group consists of children aged 6–12 yearsin primary schools in Ilesa, a semi-urban communityin Osun state, Western Nigeria. Ilesa Township, ismade up of two local governments with one having 15primary schools (with an average population of 5,000students) and the other having 17 primary schoolswith an average population of 5,000 students makingand an average primary school students’ populationof 10,000 for the town. This community was chosen asa compromise and to eliminate, to an extent, thedifference between the rural and urban communitiesin Nigeria. Because of the semi-urban nature of thetown, the students are from different socio-economicstrata, ethnic (mainly Yoruba, Hausa and Igbo ethnicgroup) and religious groups (Christianity and Islam)in the country.

j Sampling technique and sample size

A multi-staged sampling technique was adopted. In thefirst stage, the schools were stratified according to thelocal government area and subsequently 8 schools wereselected by simple random sampling from each of thelocal governments, giving a total of 16 schools. In thesecond stage, each school had two classes randomlychosen from each of the six levels of primary school.This makes a total of 12 classes per school and 192classes overall. In the third stage, the research assis-tants randomly selected 6 pupils per class based ontheir numbers in the class register. This gives a totalsample of 1,152 pupils (representing about 12% of thetotal population of primary school pupils).

j Measures

The Vanderbilt ADHD Teacher Rating Scale(VARTRS) [22] enables teachers to report on ADHDsymptoms and some common co-morbid complica-tions. Teachers rate 35 symptoms and eight perfor-mance items. The 35 symptoms consist of fourgroups, two measuring ADHD and two measuringco-morbid conditions: (a) all the nine DSM-IVbehaviours for inattention, (b) all the nine DSM-IV

A.O. Adewuya and O.O. Famuyiwa 11ADHD in Nigerian children

symptoms for hyperactivity/impulsivity, (c) anabbreviated 10-item scale for oppositional defiant andconduct disorders, and (d) an abbreviated 7-itemscale for anxiety and depressive symptoms form thepaediatrics behaviour scale [12]. Teachers rate eachsymptom on frequency (0 = never, 1 = occasionally,2 = often, and 3 = very often). When symptomscount are needed, symptoms that occur ‘‘often’’ or‘‘very often’’ are considered as present, and those thatoccur ‘‘never’’ or ‘‘occasionally’’ are considered ab-sent.

The school performance section evaluates func-tioning in the classroom with the eight items havinga 5-point likert scale. Three items evaluate academicperformance (reading, mathematics and writtenexpression), and five items evaluate classroom per-formance (peer relations, following directions, dis-rupting classes, assignment completion, andorganisational skills). Scores of 2 or 1 (somewhatproblematic or problematic) were counted as indi-cating dysfunction.

Past research on the VADTRS includes assessmentof reliability, validity and factor structure [22].

Vanderbilt Attention-Deficit Hyperactivity DisorderDiagnostic Parent Rating Scale (VADPRS). TheVADPRS is the parent version of VADTRS [22]. Itincludes all of the DSM-IV criteria for ADHD-18,ODD-8, and CD-15, and a sample of seven criteriafrom the paediatric behaviour scale that screens foranxiety and depression. The wordings have beensimplified so that the reading level is much lower thanthe teachers’ scale.

The performance section of the VADPRS is an8-item scale with four items relating to academicperformance and four items evaluating relationships(peers, siblings, parents, and participation in or-ganised activities). The parents rate each of these ona 5-point likert scale from ‘‘problematic’’ to ‘‘aboveaverage’’.

The VADPRS was translated into the local Yorubalanguage by a team consisting of a psychiatrist and alinguist. The wordings were refined to best reflect theclinical meanings of the symptoms and precise idio-matic equivalents were also considered as far aspossible. The back translation, which was performedindependently by another team consisting of a psy-chiatrist and a linguist blind to the first translation,were compared and found to be satisfactory.

Added to the VADPRS was the age of onset andduration of symptoms.

j Design and Procedure

The Ethics and Research Committee of the ObafemiAwolowo University Teaching Hospitals Complex

approved the study protocol. Approvals were grantedby the local Schools’ Board and the head of theindividual schools. Based on the method to be used incollecting data, a two-staged procedure was adopted.

In the first stage, research personnel held meetingswith the teachers of the chosen classes to explain thestudy and to review the VARTRS and its use. Theteachers were told to rate the symptoms in schoolsettings alone. Of the 192 class teachers recruited,only 187 participated in the first stage of the proce-dure. Each of them completed the VARTRS on theselected six pupils in their class giving a total of 1,122rating scales completed. Excluded from this groupwere pupils who have autism or other cognitivedisabilities and impairment not due to ADHDsymptoms. Only the pupils having at least three ormore ADHD symptoms plus some impairmentaccording to the class teacher qualify for the secondstage which was the follow-up rating by the parents.This approach mirrors the scoring algorithms used inthe Diagnostic Interview Schedule for Children(DISC) Version IV [20], where impairment questionsare omitted for children with fewer than 3 symptoms,thus eliminating any chance that they could beclassified as a case.

The follow up began with the research personnelinviting the mothers of the eligible pupils to schoolthrough the class teachers. Informed consent was takenfrom the parents after the aims and objectives of thestudy had been explained to them. Research assistantsthen reviewed both the English and the translatedYoruba versions of the VADPRS with the mothers. Theresearch assistants ensured that the mothers under-stood the items. The parents were told to rate thesymptoms in home and non-school community set-tings. The parents completed either the English versionor the translated Yoruba version. For parents who wereilliterate, one of the research assistants read the ques-tions and options aloud and ticks their responses. Theparents who did not honour the invitation to schoolwere visited at home by the research personnel forconsent and completion of the questionnaire.

j Data analysis

The Statistical package for the Social Sciences11(SPSS.11) program was used for statistical analysis.Results were calculated as frequencies (%), means andstandard deviations. Pearson’s Chi Square was used incalculating differences between groups. All tests were2-tailed, and the level of significance was set atP < 0.05. A diagnosis of ADHD is made when parentor teacher reports six or more symptoms; otherrespondent reports three or more symptoms; bothreport impairment.

12 European Child & Adolescent Psychiatry (2007) Vol. 16, No. 1� Steinkopff Verlag 2006

Results

j Demographic details

Out of the 1,122 pupils assessed with VARTRS bythe teachers, only 382 met the criteria for the follow-up rating by the parents. However, only 372 (97.4%)parents consented and filled the VADPRS. Thereforethe total number of pupils used for this study was1,112. The VARTRS scores of the 10 pupils, whoseparents declined to participate, were not signifi-cantly different from those whose parents partici-pated.

The average age of the pupils in years is 8.94(SD = 2.10). There were 682 (61.3%) boys. The par-ents include 359 (96.5) mothers, 10 (2.7%) fathers and3 (0.8%) relatives.

j Prevalence of ADHD

The six months prevalence of each of the subtypes ofADHD is shown in Table 1. The 97 pupils that met thecriteria for ADHD consist of 55 (56.7%) inattentivesubtype, 13 (13.4%) hyperactive/impulsive subtypeand 29 (29.9%) combined subtype. There were sta-tistically significant gender difference in the rates oftotal ADHD (X2 = 11.425, df = 1, P = 0.001) andinattentive subtype (X2 = 5.513, df = 1, P = 0.019)whereas no gender difference was found with thehyperactive/impulsive subtype (X2 = 3.007, df = 1,P = 0.083) and combined subtype (X2 = 2.651, df = 1,P = 0.103). The mean age of onset of symptoms inyear is 4.39 (SD = 1.06).

j Co-morbid conditions

The most common co-morbid condition was oppo-sitional deviant disorder (ODD) with 25.8% while theleast co-morbid condition was conduct disorder (CD)with a rate of 9.3%. The full percentages of conditionsthat co-morbid with the diagnosis of ADHD and itssubtypes are outlined in Table 2.

Discussion

This study, to our knowledge, was the first to deter-mine the prevalence rate of ADHD and co-morbidconditions in sub-Saharan Africa. Our main findingsinclude the prevalence of 8.7% for ADHD in oursample of primary school children aged 6–12 yearsold. This figure is comparable with the 5–10%reported in studies in western culture [9, 19] and 8.1%reported in Turkey [8]. It is however lower than the15% reported in some other none western cultureslike Israel and Columbia [5, 6] and higher than the6.9% reported in Australia [10]. The prevalence ofADHD in our sample of school children was muchhigher than the 1.5% obtained among Ethiopianchildren [3]. Several methodological differences couldaccount for this. We had used self-report instrumentswhereas the Ethiopian study had used clinical inter-views. We also included both the parent and theteacher’s report whereas the Ethiopian study hadobtained informations from the parents alone.

Our findings support the notion that ADHD is nota cultural construct as it has been debated [7, 21].Rather it seemed that the varying rates in prevalenceworldwide might be attributed to methodologicaldifferences in criteria used to define the disorder [9].It is true that the expectation and tolerance behav-iours vary in different cultural groups [13] and dif-fering attitudes of parents, clinicians, and societyaround the world towards acceptable behaviour mayinfluence diagnosis of ADHD. However, there isgrowing evidence that when the same methodology isapplied, the prevalence of ADHD do not vary signif-icantly across cultures [9].

We found the inattentive subtype to be the mostcommon in this study accounting for 56.7%. Similar

Table 1 The six month prevalence of ADHD and its subtypes among primaryschool pupils aged 6–12 years in Nigeria

Subtype Male(n = 682)

Female(n = 430)

Total(n = 1,112)

Inattentive 42 (6.2%) 13 (3.0%) 55 (4.9%)Hyperactive/impulsive 11 (1.6%) 2 (0.5%) 13 (1.2%)Combined 22 (3.2%) 7 (1.6%) 29 (2.6%)Total 75 (11.0%) 22 (5.1%) 97 (8.7%)

Table 2 Conditions that co-morbid with diagnosis of ADHD and its subtypes among primary school pupils aged 6–12 years in Nigeria

Co-morbidconditions

ADHD-Inattentive(n = 55)

ADHD-Hyperactive/impulsive(n = 13)

ADHD-combined(n = 29)

ADHD-Total(n = 97)

Oppositional defiant disorder 12 (21.8%) 4 (30.8%) 9 (31.0%) 25 (25.8%)Conduct disorder 3 (5.4%) 2 (15.4%) 4 (13.8%) 9 (9.3%)Anxiety/depression 13 (23.6%) 2 (15.4%) 5 (17.2%) 20 (20.6%)

A.O. Adewuya and O.O. Famuyiwa 13ADHD in Nigerian children

results were reported in US [22], Australia [10, 11]and Israel [5]. This was however in contrast to studiesin South America [6, 17] which had found the com-bined subtype to be the most common. Cultural fac-tors may have a role in modulating the clinicalmanifestation, rather than the prevalence of ADHD.

Co-morbid conditions were highly prevalent in oursample of children with ADHD. The ODD was themost common co-morbid problem especially with thehyperactivity/impulsive and combined subtype whileanxiety/depression was more associated with inat-tentive subtype. This association had earlier beenfound in other studies [22] with the more internalis-ing (anxiety and depression) symptoms co-occurringwith the inattentive subtype and the more external-ising symptoms (ODD and CD) co-occurring with thehyperactive/impulsive subtype.

Gender difference had been noted in the paststudies of ADHD. In our study, we found a male tofemale prevalence ratio of 2:1 across the subtypes ofADHD except hyperactivity/impulsive type which hada ratio of 3.2:1.

Overall, our findings suggest that ADHD is a crosscultural phenomenon. A strict adherence to a uniformprocess to evaluate children presenting with the core

symptoms of ADHD is warranted to minimise thedifferences in the prevalent rates.

This study was limited by several factors. First oursample size was moderate. We had used rating scalesinstead of a clinical diagnostic interview. However,the DSM-IV specific rating scales had been found tohave a high specificity and sensitivity. We hadassessed school pupils in one semi-urban town, sogeneralising the findings to a multiethnic and multi-cultured country such as Nigeria and Africa as awhole remains speculative.

The strength of our study lies in been the first toassess the prevalence of ADHD in sub-Saharan Africa.We had used both the teachers and parents as sourcesof information and we had adhered to the DSM-IVcriteria for diagnosing ADHD.

Our findings suggest that ADHD occurs acrosscultures. It also provides a broad view of ADHD inNigerian school children. This study can serve as aplatform for future analytical studies about thischallenging research issue. Given the prevalent rate,efforts should be made to map out strategies for earlyidentification and referral of these children for properevaluation and treatment.

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A.O. Adewuya and O.O. Famuyiwa 15ADHD in Nigerian children