Attention Deficit Hyperactivity Disorder (ADHD) Among Longer-term Prison Inmates is a Prevalent, Persistent and Disabling Disorder

Ylva Ginsberg; Tatja Hirvikoski; Nils Lindefors


BMC Psychiatry. 2010;10(1) 

In This Article


The present study included an estimation of the prevalence of ADHD among longer-term prison inmates. Further, it included a description of ADHD and executive functions among prison inmates compared with ADHD among psychiatric outpatients and healthy controls. The Regional Ethical Board in Stockholm approved the studies. Participants provided written informed consents before study procedures.


Norrtälje Prison is a high-security prison placed outside Stockholm, Sweden, serving the entire country, hosting 200 adult male inmates. The prison holds mainly longer-term inmates, typically convicted of crimes because of drugs or violence.

Figure 1 shows the study flowchart. Norrtälje Prison hosted 589 inmates between December 2006 and April 2009. Of those inmates, we did not invite 200 for screening, as we could not include them in the following trial because of deportation out of the country after served conviction. Further, we did not approach 74 inmates because of practical reasons, or if we considered them as too mentally affected to take part. Thus, a specially trained correction officer successively approached 315 prison inmates for screening during the study period. Another purpose of screening was to identify subjects for a diagnostic evaluation for ADHD before recruitment for a clinical trial. Therefore, we ended recruitment as we had randomised all 30 subjects for the trial in April 2009.

Figure 1.

Flow chart of the screening procedures and diagnostic assessments.

Following the screening survey, we performed extensive diagnostic assessments for ADHD and coexisting disorders among a group of inmates. We selected subjects first according to their origin, as the Stockholm County Council funded the assessments as part of regular clinical practice. Thus, we invited all prison inmates marking adult ADHD by the screening, registered in the Stockholm County, with at least 14 months left to conditional release, and approved by the security officers to stay at the ADHD ward. By this pre-screening, we evaluated if subjects with ADHD would fulfil criteria for taking part in the following clinical trial with methylphenidate (Ginsberg and Lindefors, unpublished data). Subjects with coexisting disorders, such as ASD, anxiety and depression could take part if considered stable by the investigator at the assessment. Further, the general cognitive functioning had to be above the level of mental retardation. In addition, subjects could continue stable pharmacological treatment for coexisting disorders if we did not suspect treatment interfering with methylphenidate. Additionally, subjects had to be free from serious medical illnesses. Thus, after meeting criteria for the following trial and providing a written informed consent, the subject could take part in the diagnostic evaluation.

We considered 47 prison inmates for assessment. However, we excluded one subject because of an exclusion criterion, whereas six subjects denied taking part. Of 40 consented subjects, six dropped out during the assessments. Therefore, we finally assessed 34 subjects and could confirm ADHD among 30 of them (Figure 1). When appropriate, we extended the evaluation to confirm ASD in consistence with DSM-IV. We defined ASD as fulfilling the criteria for Autistic syndrome, Asperger syndrome or Pervasive developmental disorder, not otherwise specified (PDD-NOS). This evaluation included the Asperger Syndrome Screening Questionnaire (ASSQ),[13] the Diagnostic Interview for Social and Communication Disorders (DISCO),[14,15] and the Autism Diagnostic Observation Schedule (ADOS), module 4.[16]

The psychiatric outpatient study group comprised 20 adult men with ADHD, 18 of them with ADHD of the combined type, and two with the predominantly inattentive subtype. We consecutively recruited these subjects to another study[17] between 2004 and 2006, from the Neuropsychiatric Unit, Karolinska University Hospital; a psychiatric outpatient tertiary unit specialised in ADHD. Notably, the exclusion criteria for taking part were different among psychiatric outpatients, as ongoing pharmacological treatment for coexisting disorders, APD, ASD, 70 > IQ < 85, or pure 'sluggish, inattentive' ADHD[18,19] excluded. Because of different criteria, we expected a difference in IQ between groups. Thus, we controlled for IQ in the statistical analyses of executive functions.

The control group[17] comprised 18 adult healthy males not needing psychiatric care, assessment for learning difficulties or educational support during childhood. Further, they did not need psychiatric care during the present study. We recruited age-matched controls from advertisement on fitness training centres in Stockholm City and among friends of staff-members.


Estimation of ADHD Prevalence among Longer-term Prison Inmates WURS is a 61-item self-administered scale for rating frequencies of ADHD childhood symptoms and behaviours retrospectively on a 5-point scale, from 0 = not at all or slightly, to 4 = very much. The subscale WURS-25 provides a total sum score (range 0–100) by summing those 25 items best discriminating between ADHD and controls.[20] According to the originators, a cut-off score of 36 is 96% sensitive and specific for identifying childhood ADHD among the general population.[20]

The ASRS-Screener comprises the 6 out of 18 most predictive items of the Adult ADHD Self-Report Scale (ASRS)[21] for defining present ADHD in adulthood. Fulfilling at least 4 out of 6 significant items[22] on ASRS-Screener defines adult ADHD. Both scales are standard tools in clinical practice, despite the lack of Swedish validations. In this study, we defined adult ADHD as reaching the cut-off levels for WURS-25 and ASRS-Screener, respectively.

Assessment for ADHD among Prison Inmates Board certified psychiatrists and clinical psychologists well experienced in ADHD, conducted the clinical assessments. We confirmed ADHD in accordance to DSM-IV.[23] The evaluations included a semi-structured clinical diagnostic interview for ADHD based on the DSM-IV-criteria.[23] Further, ASRS[24] is an 18-item self-administered scale with appropriate psychometric properties[25] based on the DSM-IV criteria and adjusted to reflect ADHD symptoms as seen in adults.[22] We used a non-validated Swedish version of the ASRS[24] for rating symptom frequencies on a 5-point scale, from 0 = never; to 4 = very often, providing a total sum score (range 0–72).

Whenever possible, we collected collateral information from parents or other significant others by questionnaires, before psychologists or psychiatrists performed interviews. The questionnaires included the Five to Fifteen (FTF) questionnaire[26,27] and the Conners' Brief Parent Rating Scale - Conners' Hyperactivity Index,[28,29] respectively.

The Five to Fifteen (FTF) questionnaire[26,27] elicits childhood symptoms and developmental problems of ADHD and coexisting disorders in the ages five to fifteen years. The FTF shows acceptable to excellent inter-rater and test-retest reliability and comprises 181 items scored on a 3-point scale, from 0 = does not apply, to 2 = definitely applies.

The Conners' Brief Parent Rating Scale - Conners' Hyperactivity Index is validated in several countries. This scale describes ADHD and oppositional defiant symptoms and behaviours in children up to 10 years of age,[28] comprises 10 items, scored 0–3, and provides a total sum score (0–30).

We collected additional collateral information by medical records from child- and adolescent psychiatry, school health services, adult psychiatry and forensic psychiatry. Further, we evaluated coexisting disorders by the Structured Clinical Interview for DSM-IV Axis I Disorders (SCID I),[30] the Hare Psychopathy Check List-Revised (PCL-R), a semi-structured interview defining psychopathy by a total sum-score ≥ 30,[31] and the self-rated version of the Structured Clinical Interview for DSM-IV Axis II personality disorders, the SCID II Patient Questionnaire (SCID II PQ). We estimated frequencies of personality disorders by increasing the screening cut-off level for each personality disorder by one score. This procedure has shown an acceptable agreement with the SCID II interview.[32] Furthermore, the evaluation comprised a medical history, physical examination, routine laboratory tests, urine drug screening and a neuropsychological test battery assessing IQ and executive functions. As prison inmates often present learning disabilities such as reading difficulties,[9] we assessed neuropsychological tests not requiring reading, writing or mathematic skills. We estimated IQ by the Wechsler Adult Intelligence Scale-III subtests Vocabulary and Block Design, a dyadic short form correlating 0.92 with WAIS-III FSIQ.[33,34]

Neuropsychological Tests of Executive Functions Digit Span[33] measures verbal working memory (WM) whereas Span Board[35] measures visuospatial WM. Further, we measured sustained attention, impulse inhibition and other executive functions by the computerized The Conners' Continuous Performance Test II (CCPT).[36] The CCPT measure Hit RT reflects basic reaction time, whereas Hit RT SE, Variability, Hit RT block change, Hit SE block change, Hit RT ISI change, Hit SE ISI change and Perseverations reflect variability dependent measures. Finally, Omission errors, Commission errors, Detectability (d'), and Response style (â) reflect accuracy dependent measures.

Assessment for ADHD among Psychiatric Outpatients The diagnostic evaluation comprising neuropsychological tests was similar as among prison inmates. However, we did not assess SCID I, SCID II PQ, or PCL-R among ADHD psychiatric outpatients. Case files provided information on psychiatric comorbidity. Besides, the self-rated Beck Depression Inventory,[37,38] the Beck Anxiety Inventory,[39] and the Current ADHD Symptom Scale - Self-Report Form,[40] evaluated present psychiatric symptoms.

Healthy Controls We interviewed controls for confirming the absence of learning difficulties or psychiatric problems during childhood and the study, respectively. Further, we used the same self-rating scales for present psychiatric symptoms as among the psychiatric outpatients. Finally, the neuropsychological tests were similar as for the other groups.

Statistical Analysis

Descriptive statistics summarised demographic data and clinical characteristics of subjects. We carried out inferential statistics by analyses of variance (ANOVA), Student's t-test or Mann-Whitney U-test for continuous measures, and chi-square test or Fisher's exact test for categorical measures. Further, for comparing between groups on neuropsychological measures, we performed a series of analysis of variance (ANOVA) with Bonferroni corrected post hoc comparisons, whenever main analyses reached significance. In addition, we aimed to control for IQ differences. Thus, we reanalysed measures of executive functions (DS, SB, and CCPT) by performing a series of ANCOVA with the dyadic estimated IQ entered as a covariate. By these analyses, we evaluated if lower IQ among prison inmates could explain their executive dysfunctions. We present statistics from both ANOVAs and ANCOVAs, as most measures of executive functions did not co-vary with IQ. We set the alpha-level at p = .05. Finally, we performed all statistical analyses by SPSS 17.0 and 18.0, respectively.


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