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Analysis of the Conners Continuous Performance Test for use in ADHD, language-based learning disorders and a comorbid group

ProQuest Dissertations and Theses, 2009
Dissertation
Author: Jeanette R Froncillo
Abstract:
The purpose of this study was to examine the effectiveness of the Conners Continuous Performance Test (CCPT) in distinguishing between children and adolescents with Attention-Deficit Hyperactivity Disorder (ADHD), Language-Based Learning Disorders (LBLDs), and a mixed group carrying both diagnoses. The CCPT is a computerized test of attention used by clinicians both in research and diagnosis. Literature has shown that the CCPT can distinguish children and adolescents with ADHD from normal comparison groups and suggests children and adolescents with LBLDs show behavioral characteristics that are similar to those exhibited by children and adolescents with ADHD. Some of the processes used for attentional control are also used in language-based learning, with both disorders sharing effects on executive functions. The current study used the archival data of 197 children and adolescents who underwent neuropsychological testing for learning difficulties and/or problems with attention at a clinic in New England that specializes in neuropsychological and learning disability assessment. It was originally hypothesized that a discriminant analysis of several measurement scores on the CCPT of these children and adolescents would distinguish between individuals diagnosed with ADHD, a LBLD, or those diagnosed with both. After consultation with my project committee, it was decided that this type of analysis did not fit with the data. Analysis of Variance and Chi Square Analysis were used to answer both the primary question posed in this study and several other secondary questions related to the performances of each group on the CCPT and in the literature. It was found that clinician diagnosis did not match CCPT Certainty Percentage Index (which indicates the strength of the individual's profile for a clinically significant or non-clinically significant attention problem. However, the CCPT was useful in differentiating the ADHD group from the LBLD and Mixed groups, not only on the Certainty Percentage Index, but also for Hit Reactions Times, Omission error percentages, and Commission error percentages.

Table of Contents Acknowledgments iv Abstract vi List of Tables xii List of Figures xiii CHAPTER I: INTRODUCTION 1 LITERATURE REVIEW 6 Conners Continuous Performance Test (CCPT) 6 Definition 6 History 7 Assessment 10 Current Research 11 Attention-Deficit Hyperactivity Disorder (ADHD) 12 Definition 13 Incidence and Prevalence 14 History 14 Behavioral Manifestations 15 Theories 17 Risk Factors 20 Course 20 Assessment 21 Current Research 23 Treatment 24 CCPT and ADHD 27 Language-Based Learning Disorders (LBLDs) 27 Definition 27 History 30 Incidence and Prevalence 31 Behavioral Manifestations 31 Theories 32 viii

Risk Factors 33 Course 34 Assessment 35 Current Research 37 Treatment 38 CCPTandLBLDs 41 Comorbidity of ADHD and LBLDs 42 Definition 42 History 42 Behavioral Manifestations 42 Incidence and Prevalence 42 Theories 42 Risk Factors 42 Course 45 Assessment 45 Current Research 51 Treatment 55 CCPT and Comorbidity of ADHD and LBLDs 55 CHAPTER III: METHOD 56 Research Design 56 Participants 56 Measures 57 Conners Continuous Performance Test 57 Procedures 58 Participant Consent 58 Selection of Records 58 Data Collection and Storage 59 Proposed Data Analysis 59 CHAPTER IV: RESULTS 60 Participant Demographics 60 IX

Data Analysis 62 Analysis of Variance on CCPT Certainty Percentages, Clinician Diagnosis and Gender 63 Sample Means and Standard Deviations for Gender and Diagnosis.... 64 Effects of Gender 65 Diagnosis and CCPT Certainty Index 66 Hit Reaction Times across Diagnostic Group and Gender 68 Analysis of Omissions by Diagnostic Group and Gender 69 Sample Means and Standard Deviations for Commission errors on CCPT by Gender and Diagnosis 71 Analysis of Commissions on CCPT by Gender and Diagnosis 72 CHAPTER V: DISCUSSION 75 Review of the Study 75 Unexpected Occurrences/Events 80 Interpretation of Results 80 Strengths and Weaknesses of Research Design 83 Ethical Issues 84 x

Recommendations for Future Research 84 Summary and Conclusion 86 APPENDICES 88 Appendix A: Interpreting Conners CPT Results 89 Appendix B: Sample Conners Report 91 Appendix C: Conners CPT Measures and Definitions 97 Appendix D: DSM-IV Criteria for the Diagnosis of Attention-Deficit Hyperactivity Disorder 99 Appendix E: DSM-IV Criteria for the Diagnosis of Learning Disabilities Appendix F: CCPT Data Sheet 101 Appendix G: Test Battery used for Assessment 103 Appendix H: Agency Letter of Permission 104 REFERENCES 109 xi

List of Tables Title Gender Distributions by Age and Diagnosis 62 Group Means on Certainty Percentage Index Across Gender and Diagnosis 64 Analysis of CCPT Certainty Index Percentage Across Diagnostic Groups and Gender 66 Analysis of Confidence Index Classifications Across Diagnostic Group and Gender 67 Chi-Square Analysis for the Effects of Diagnosis And Gender 67 Analysis of Hit Reaction Times Across Diagnostic Groups and Gender 68 Hit Reaction Times by Diagnostic Group 69 Analysis of Omissions Across Diagnostic Groups And Gender 70 Descriptive Analysis of Percentage of Omissions By Diagnosis on CCPT 70 CCPT Percentage of Omissions by Diagnosis and Gender 71 Analysis of Commission Errors on the CCPT Across Diagnostic Groups and Gender 72 CCPT Percentage of Commissions by Diagnosis 73 Gender Effects by Diagnosis and CCPT Commission Percentage 73 xii

List of Figures Number Title 1 Frequencies of Ages of Participants by Year 60 2 Mean Differences in Confidence Across Diagnosis And Gender 65 xiii

CHAPTER 1 INTRODUCTION Hi, my name is Leah and I am 9 yers old, I'm in the forth grad, my faveret coler is pink, I wont to be in the nwba, is the nasinal wimen bacikball ashoceashen My furit subject in school is sciyens My whorst subjet is shochat stateys. My warst subjets are reding and riting. I like siyen the most because we do lost of esperas and this week we are we wit insed and fish to see hou thay beyhave, my wast subt with red is because I have trubl sonding out leteh sonds. I have trubl riding becus I have trulb sorting out werds whal spelling. Riding and riding mack me fell like I can't be a vet when I get older because vets have to red and rhiyt a lot. What I what for my fuheu is to be come a nwba payer and a part time vet. The passage as read by Leah. Hi, my name is Leah, and I am 9 years old. I'm in the fourth grade. My favorite color is pink. I want to be in the NWBA. It is the National Women's Basketball Association. My favorite subject in school is science. My worst subject is social studies. My worst subjects are reading and writing. I like science the most because we do lots of experiments and this week we are with fish and insects to see how they behave. My worst subject with reading is because I have trouble sounding out letter sounds. I have trouble writing because I have trouble sorting out words while spelling. Reading and writing make me feel like I can't be a vet when I get older because vets have to read and write a lot. What I want for my future is to become an NWBA player and a part-time vet. Leah was someone I had the opportunity to observe over several years. I became a participant/observer in her physical, psychological, and intellectual growth. In pre-school Leah was behind her peers in learning the alphabet and although she loved to hear Dr. Seuss books, she could not provide rhyming words herself. She was distractible, impulsive, and constantly on the move. When it came to learning something, she would repeatedly attempt to figure it out in an unorganized, trial-and-error fashion and then become frustrated when she still could not do it. In addition, she appeared to either ignore directions, or she would go on with her attempts as if she had not heard the directions. After entering first grade, Leah consistently performed below grade level in reading and 1

writing, and teachers sent notes home regarding her restlessness and inability to pay attention. Leah's own attitude to schoolwork indicated stress and anxiety; she would sometimes hide undone homework assignments or lie to her mother that she did the assignment during school. When she did do homework, she often rushed through it, making careless mistakes as a result. Study Rationale My professional work involves neuropsychological assessment of presenting complaints of attention/distractibility, hyperactivity, and/or difficulty learning in a specific area like reading, writing, or math. It was my initial impression that Leah's difficulties involved specific cognitive and attentional difficulties, and this was later confirmed by formal assessment. The purpose of such assessments is to assign children into diagnostic groups for the purpose of creating treatment planning based on research with these groups. My curiosity regarding Leah's difficulties led me to speculate that one neuropsychological test, the Conners Continuous Performance Test (CCPT), might serve the function of making such distinctions. Conners Continuous Performance Test The CCPT is a computerized test that indicates the likelihood of a child having a significant problem with attention, and is often used in conjunction with collateral clinical data in making a diagnosis of Attention-Deficit Hyperactivity Disorder (ADHD). It generates scores indicating with a high, moderate, or low degree of certainty whether there is a clinically significant problem in attention. The CCPT was originally designed for the identification of neuropsychological deficits in psychiatric populations. The test's 2

requirement for control of attention, however, prompted its use for ADHD research (Epstein et al. 2003). ADHD is the most common neurobehavioral diagnosis in children (Furman, 2005), with the frequency of the diagnosis increasing (Conners, 2000). Reviews of epidemiological studies suggest that ADHD is associated with long-term disability, psychosocial difficulties, and symptom persistence into adulthood (Scahill & Schwab- Stone, 2000; Taylor, 1998). Though there is a wide margin in the literature on the definition of what constitutes impairment, learning disabilities in general occur in children diagnosed with ADHD in an estimated range of 12%-60% (Furman, 2005), with Reading Disability, a language-based learning disorder (LBLD) occurring in 35%-50% of cases (Kaplan & Dewey, 2006). Among children diagnosed with ADHD, an estimated 12%-60% also have learning disabilities (Furman, 2005), and others estimate that between 35%-50% of children with a learning disability have a reading disability, or an LBLD (Kaplan & Dewey, 2006). As stated earlier, the diagnosis of ADHD was reported by Conners (2000) to have doubled between 1995 and the year 2000. Study Purpose Due to high comorbidity and cognitive similarities, it is a difficult task to establish a differential diagnosis between learning disorders and ADHD. ADHD is considered a developmental disorder of attention affecting children and adults (Furman, 2005), and is characterized by poor attention, impulsivity, and hyperactivity (Berwid, et. al. 2005). In school, children diagnosed with ADHD are less likely than their peers to stay seated 3

(hyperactivity), wait for their turn (impulsivity), or pay attention or concentrate for a sustained amount of time (poor attention). Language-based learning disabilities (LBLDs) involve reading, writing, spelling, comprehension, and both expressive and receptive language skills. Among LBLDs, reading disability counts for an estimated 80% of all learning disorders (Shaywitz & Shaywitz, 2003). Reading and writing require language-based processes, primarily the ability to attach phonemes, or speech sounds, to the visual components of written language. The ability of children with LBLDs, to recognize these phonemic sounds is impaired and is purported to negatively affect word recognition and decoding (Mowbry & Wegner, 2005). Perhaps not surprisingly, school-aged children affected by ADHD and learning disabilities appear to have more difficulty with learning than either group alone (Mayes et al., 2000). This difficulty arises as a result of cognitive processes that are used for learning in general, those involved in learning specific academic skills like reading, writing, and arithmetic, and those involving attention. Summary The CCPT is gaining wide use in clinical and research settings and is often used in conjunction with clinical data and results from other measures to diagnose ADHD. The CCPT is potentially able to accurately identify differences between attention disorders, learning disorders and a combination of both because it breaks the concept of attention down into components, like number of omissions, number of commissions, reaction times, sustained attention, and others, that are additionally involved in learning. 4

The CCPT has been shown to differentiate children with ADHD from normal controls. In this thesis, the CCPT data of a large number of children and adolescents from a clinic specializing in learning disorders was analyzed to see if CCPT Certainty Percentage Indices corresponded to the diagnostic classification given by the assessing clinician for each of the study groups. The current study also examined Hit Reaction Times and error percentages of Omissions and Commissions on the CCPT for differentiation of the clinician diagnostic groups, and any effects for gender. 5

CHAPTER 2 LITERATURE REVIEW This chapter will be divided into four sections. In the first section, I will focus on a literature review of The Conners Continuous Performance Test, including the history of the test, its past and current application in research and treatment, and its proposed function in the present study. In the following sections I will explore Attention-Deficit Hyperactivity Disorder (ADHD), Language-Based Learning Disorders (LBLDs) and finally, a comorbid group. I will discuss the incidence and prevalence of each diagnostic group, give a history of the disorder, including current diagnostic criteria and assessment, and outline the role CCPT has played in the research conducted on each of the disorders. Biological (including genetic) influences and risk factors for each disorder will be discussed, as well as current treatment options. Finally I will discuss the use of the CCPT in the proposed study in distinguishing each of the diagnostic groups discussed. Conners Continuous Performance Test (CCPT) Definition The CCPT is a computerized vigilance test used in research and clinical settings (vigilance is defined here as focused attention). It is designed to measure lapses in attention by signal detection. The CCPT comes in several formats. The present study uses the standard version, in which the participant must press a key for every letter presented on the screen except for the letter X. The letters are presented in differing time blocks that vary both the time between the presentation of a letter and the length of time the letter is presented, 1,2, or 4 seconds (Conners, 1992, 1995). 6

Measurements gathered from this test include the number of correct responses, the number of incorrect responses, various reaction times, and the consistency of performance (or vigilance) to the task, over time. The test takes approximately 14 minutes to administer (Perugini et al., 2000) and generates a computerized report that includes helpful charts, graphs, and guidelines for interpretation. (See Appendix A for interpretation guidelines). History Historically, the Continuous Performance Test and its acronym, CPT, were first introduced in 1956 by researchers to detect lapses in attention caused by seizures among people with petit mal epilepsy. The exploration of its use in clinical settings led to studies of attention and the test was then expanded to include measurement of the effects of different signal detection parameters on attention in different populations (Conners, 1992, 1995). The result has been a family of tasks that have similar characteristics but that vary in the stimulus and response patterns chosen by the examiner. Riccio et al. (2002) report that since the 1950s, the CPT, which has several different versions, has been shown to be a sensitive indicator of brain dysfunction or damage with regard to the attentional system. It has also been shown to be symptom- specific with regard to attention disruption, but not necessarily disorder- specific. The test measures lapses in attention by measuring parameters like response inhibition, impulsivity, or inattention, and by recording time lapses between signal presentation and the individual's response patterns. The authors (2000) point out, however, that this does not mean that test results can isolate a specific disorder. They report that their findings 7

have been replicated with different versions of the CPT as well as with different populations, and that they have helped validate CPTs in general. Interpretation of the CCPT is based on four sections that are generated from the data provided by the test. The first section describes the measures the CCPT provides (See Appendix C for a list of the CCPT measures and their definitions). The second section describes the use of statistics like T-scores and percentiles, while the third section describes ways in which the CCPT measures are grouped for data interpretation. The fourth, and final section, presents case studies as examples of how the data are used in interpretation and how the test is incorporated with other clinical assessment data that includes peripheral information from parents, teachers, and pediatricians (Conners, 1992, 1995). Much of the information provided by the CCPT is converted into T-scores and percentiles to aid in interpretation. T-scores represent the individual participant's score in relation to the scores of the comparison group or a control group. T-scores have a mean of 50 and a standard deviation of 10, so that a T-score of 60 would represent a performance that falls one standard deviation above the average. T-scores of 60 and above on all measures of the CCPT suggest a problem with attention (Conners, 1992, 1995). Percentiles are used to compare a participant's performance relative to the comparison group. For example, if a child falls into the 50th percentile, it means that 50% of the comparison group scored lower than the test subject and 50% scored higher. The higher the number of measures on the CCPT indicating a problem, the stronger the evidence for a diagnosis of attention difficulty. The calculations used for creating T- 8

scores and percentiles are based on a comparison of individuals of the same age and gender. Examples of the CCPT measures that indicate an attention problem are omission errors, hit reaction times, standard errors, and changes in performance over time. Omission rates that are high suggest that the participant is not attending to the task, with percentiles above 90 indicating inattentiveness. Slow reaction times combined with high error rates also indicate inattentiveness. A T-score of 40 or lower is considered a slow hit reaction time. Attention problems are indicated when a participant has a Standard Error T-score of 60 or higher, which is a strong indication of an inconsistent response style. Inattention is also indicated when atypical response speed slows as the test progresses or responses are less consistent over time. Important changes in response over time are indicated by T-scores of 60 or more (Conners, 1992,1995). Samples used in cross-validation for the CCPT were gathered from independent investigative teams and with data from Dr. Conners' clinic. Additional participants matched for sex and age were taken from the general population. Conners states that the CCPT is likely most effective for 6-17 year old individuals (1992, 1995). Conners adds that there are two purposes for the CCPT. First, it is an aid in the identification of attention problems, and second, it should provide a good way to monitor the effectiveness of treatment, in this case pharmacological treatment. 9

Clinical Use/ Neuropsychological Assessment The expansion of the CCPT included a wide variety of research on the assessment of attention and its value in clinical use has been explored in numerous studies. Labruna's use of the CCPT (1998) showed differentiation between children with ADHD from both a normal and a psychiatric comparison group. He found that children with ADHD are more impaired on measures of response inhibition than children in the comparison groups. ADHD children also showed impairment in impulsivity and accuracy by comparison with the normal group. Labruna's findings support the theory that behavioral inhibition is a core deficit in children with ADHD. Observations of children engaged in the CCPT showed omission errors occurring as a result of off-task behavior and impaired inhibitory response to non-task stimuli (1998). In 1990, Levy and Hobbes did a study comparing children diagnosed with ADHD and a group of children without a diagnosis of ADHD using the CCPT. Their theory was that reaction times would be an indicator of ADHD; they proposed that reaction time is a function of processing the target and is preceded by uncertainty, which can affect response time. The results of their study showed that reaction times were reflective of attention and/or activation processes that distinguished between children with ADHD and those without, and correctly classified children 97.4% of the time. The measurements on the CCPT with the best discriminatory factors were age-normalized commission errors and age-normalized mean reaction times. This study used an earlier version of the CCPT, which did not contain many of the current version's indices that are aimed at 10

understanding the underlying processes of attention like working memory and sustained attention. While some studies report no significant association between the CCPT and other assessment measures for ADHD, such as parent/teacher rating forms, one study looked at the relationship between ADHD and other ADHD measures (Epstein et al., 2003). This study looked at specific behaviors of ADHD children and corresponding indices on the CCPT. (See Appendix C for CCPT measurements and their definitions) It was found that children diagnosed with ADHD had more variable reaction times, more errors of commission and omission, and exhibited poorer perceptual sensitivity than non diagnosed children. Specific symptom relationships between the DSM-IV criteria and CCPT parameters did demonstrate a significant relationship to ADHD symptoms. Current Research Much of the research has moved in the direction of measuring specific processes believed to be involved in the concept of attention. Studies have focused on symptoms of impaired attention like inhibition, hyperactivity, inattention, and impulsivity. In 2004, Nichols and Waschbusch examined research published since 1991 on laboratory measures for ADHD symptoms in order to review their validity. One of the measures included the CCPT. Results showed the most support for several measures, one of which was the CCPT. The authors concluded that the findings suggested a promising use for the CCPT when combined with a multi-method approach that included parent and teacher reports. Berwid et al. (2005) did a sustained attention and response inhibition study in young children who, according to parent and teacher ratings, were at risk for ADHD. 11

These children were given a CPT and were found to have ADHD-related impairment in inhibitory control and sustained attention responses, which appeared to be attributable to generalized behavioral dysregulation or poor state regulation (variability and inconsistency in performance). Reaction time variability, another measure believed to be involved in attention difficulties, has been documented in comparative studies of children with and without ADHD. Hervey et al. (2006) did a study of reaction time (RT) distributions of the CCPT in children and adolescents from an ADHD sample and compared them to a matched sample of normal controls. Their results suggest that the greater number of abnormally long RTs of children with ADHD reflect lapses in attention in some but not all trials. Basically, the children with ADHD responded differently than the control group. Their responses were slower and they had more variability in their responses than the normal control group, which was matched on gender, age, and ethnicity. When children with ADHD had a faster rate of responding, the authors suggested this was due to impulsivity and not necessarily focus on the task. The literature on the CCPT has been shown to differentiate ADHD individuals with normal controls. The following section will explore ADHD and the use of the CCPT in this population up to this point. The section will end with a brief explanation of the expected contribution of the CCPT to the current thesis. Attention-Deficit Hyperactivity Disorder (ADHD) This section will begin with a discussion of the definition of ADHD along with its incidence and prevalence. This will be followed by an exploration of the history, 12

behavioral manifestations, genetic markers/risk factors, theories, course, assessment, current research, and treatment of the disorder. The section ends with an explanation of the relevance of ADHD for the use of the CCPT. Definition The development of the diagnosis of ADHD over the past 100 years reflects the changing theoretical and scientific information regarding this diagnosis. The Diagnostic and Statistical Manual of Mental Disorders-Fourth Edition, or DSM-IV (1994), conceptualizes ADHD as exhibiting behaviors like hyperactivity, impulsivity, and inattention. In the classroom, examples of these behaviors would be a child being restless, fidgety, or unable to pay attention, so that the ability to listen or register details is impaired (Stubbe, 2000). The primary core deficits associated with ADHD were postulated in the 1980s as being the inability to regulate attention, inhibition, and impulsive behaviors. Following a range of changes in the nomenclature and definition of primary deficits, three subtypes of ADHD were identified: inattentive type, hyperactive- impulsive type, and a combined type (2000). (See Appendix D for DSM-IV criteria for a diagnosis of ADHD). It is suggested that the changes in both terminology and the diagnostic conceptualization of ADHD have influenced study design, classification, and treatment options, as well as comorbidity with other disorders. One concern in much of the research and literature on ADHD has been concerned with diagnostic uncertainty or inconsistent diagnostic findings (Stubbe, 2000). Others have suggested that because there is lack of a definitive test for ADHD, and inconsistent symptom thresholds for ADHD, there is no clear demarcation of what constitutes "disease and non-disease" (Scahill & Schwab- 13

Stone, 2000, p.542). For these reasons, there is continued debate among clinicians surrounding the definition of ADHD. For purposes of this thesis, Gordon & Keiser's (1998) definition of ADHD will be used. These authors state that behavioral disinhibition is the core symptom of ADHD. They point to what they refer to as "overwhelming evidence" (105) that individuals with this core behavioral symptom find it difficult or impossible to stop themselves from responding to irrelevant stimuli. Associated with this are impulsive behaviors that make it difficult for the individual to inhibit responding to irrelevant or distracting stimuli. Incidence and Prevalence In an exploration of the literature, prevalence estimates have a wide range. In a review of 13 epidemiological studies since 1980, that used interviews to make a diagnosis of ADHD according to DSM-III or DSM-III-R criteria, prevalence estimates are around 1.9%-14% (Scahill & Schwab-Stone, 2000). Others put rates at 3%-5% (Lueng & Lemay, 2003; Stubbe, 2000) and 2%-18% (Rowland et al., 2002). The most recent estimate found is between 4%-12% in the general population of 6-12 year olds ("New Development", 2006). Stubbe (2000) reported that symptoms of ADHD have been the primary reason for 30%-50% of school-aged children being referred to mental health services. History The seeds for the terminology and current definition of ADHD began in 1902 with George Still's description of a disorder that was not caused by brain damage or retardation, but was described as a "defect" in a child's willpower and attention ("Attention-Deficit/Hyperactivity", 2000). In the 1920s, the terminology for a "brain 14

Full document contains 143 pages
Abstract: The purpose of this study was to examine the effectiveness of the Conners Continuous Performance Test (CCPT) in distinguishing between children and adolescents with Attention-Deficit Hyperactivity Disorder (ADHD), Language-Based Learning Disorders (LBLDs), and a mixed group carrying both diagnoses. The CCPT is a computerized test of attention used by clinicians both in research and diagnosis. Literature has shown that the CCPT can distinguish children and adolescents with ADHD from normal comparison groups and suggests children and adolescents with LBLDs show behavioral characteristics that are similar to those exhibited by children and adolescents with ADHD. Some of the processes used for attentional control are also used in language-based learning, with both disorders sharing effects on executive functions. The current study used the archival data of 197 children and adolescents who underwent neuropsychological testing for learning difficulties and/or problems with attention at a clinic in New England that specializes in neuropsychological and learning disability assessment. It was originally hypothesized that a discriminant analysis of several measurement scores on the CCPT of these children and adolescents would distinguish between individuals diagnosed with ADHD, a LBLD, or those diagnosed with both. After consultation with my project committee, it was decided that this type of analysis did not fit with the data. Analysis of Variance and Chi Square Analysis were used to answer both the primary question posed in this study and several other secondary questions related to the performances of each group on the CCPT and in the literature. It was found that clinician diagnosis did not match CCPT Certainty Percentage Index (which indicates the strength of the individual's profile for a clinically significant or non-clinically significant attention problem. However, the CCPT was useful in differentiating the ADHD group from the LBLD and Mixed groups, not only on the Certainty Percentage Index, but also for Hit Reactions Times, Omission error percentages, and Commission error percentages.