ADHD has become a focus of study to improve knowledge of professionals in health and education. The investigation of the disease occurs by the atypical conditions of development with higher incidence and prevalence in the population of school age around the world. Seems to be a consensus among researchers about the definition of ADHD, which is considered a disorder of multifactorial origin, whose main symptoms are motor hyperactivity, impulsivity and attention deficit. This major triad co-occurs with secondary symptoms such as emotional disorders, learning disabilities, oppositional defiant disorder, conduct disorder, depression and anxiety (Andrade & Flores-Mendoza, 2010; Aragonès et al., 2010; Oscar & Alma, 2010; Faraone, Sergeant, Gillberg, & Biederman, 2003; Lindblad ,

Weitoft, & Hjern, 2010; Londoño, Cifuentes, & Luber, 2011) .

Pondé and Freire (2007) define the disorder as follows:

The disorder is characterized by three groups of symptoms, the prevalence of each define disease subtype: 1) predominantly inattentive, 2) predominantly hyperactive-impulsive or 3) combined. Children with ADHD may have difficulty in school, relationship problems and low selfesteem. Comorbidity with other psychiatric disorders, according the authors, can result in serious social repercussions and exclusion. (p. 241)

In other analysis there is convergence as the chronicity of ADHD. Different from the previous procedures in the treatment two decades ago, currently, researchers have focused on developing procediments of intervention strategies on different stages of life. This is important to the fact that ADHD does not qualify as a disorder of childhood and adolescence, and may persist with significant functional impact on at least 50% of cases on adulthood. The symptoms of the disorder changes with advancing age, already possible to determine which features are more common in two main stages of life, childhood and adulthood (Aragonès et al., 2010; Blázquez-Almería et al., 2005; Faraone et al., 2003; Poeta & Rosa Neto, 2004) .

Fayyad et al. (2007) state that:

It has been observed through clinical studies in children with attention- deficit/hyperactivity disorder and hyperactivity symptoms often persist into adulthood deficit. (p. 402)

Childhood is the phase that commonly identifies ADHD-like symptoms. It can be observed more frequent in frequent exchange of activities; problems in academic organization; difficulty to maintaining friendship relationship with children of the same age; accumulation of different activities; motor disturbance; impulsivity; learning disability, and often school failure (Andrade & Flores- Mendoza, 2010; Poeta & Rosa Neto, 2004; Pondé & Freire, 2007) . There are even indications that the transition to adolescence, individuals with ADHD, especially those with comorbid conduct disorder, has increased to engage in delinquent behavior trend, substance abuse and sexual risk practices (Faraone et al., 2003) . Already in adulthood, lack of attention, impulsivity, irritability and low frustration tolerance mark the life of these people, as emphasized Poet and Rose (2004) .

The prevalence of the pathology in adults is approximately 4%. North- American researchers claim that the sequelae of ADHD affects between 2% to 2.5% of adults, whom have inattention, impulsivity, irritability, intolerance and frustration. (p. 151).

If the definition of ADHD achieves a consensus in the scientific community, the same did not occur with the epidemiological findings. Some authors argue that the main problematic is the use of procedures not considering the diagnostic criteria recommended by the World Health Organization (WHO), the DSM IV, with inaccurate or nosological definitions for inadequacies in the methods of data collection (Andrade & Flores-Mendoza, 2010; Blasquez-Almería et al., 2005; Faraone et al., 2003; Pineda, Lopera, Palacio, & Castellanos, 2001) .

Regarding this matter Montiel-Nava, Peña and Montiel-Barbero (2003) highlight:

The prevalence of the disorder, attention deficit hyperactivity disorder (ADHD) is a condition with greater variability in different published epidemiological studies. Data on the prevalence of ADHD vary substantially from country to country and offer a range of heterogeneous data that describe the same clinical syndrome in children. Several epidemiological studies in different countries that use different classification and diagnosis (ICD-9, ICD-10, DSM-III-R, DSM-IV) systems, data indicated prevalence controversial. (p. 815)

The data on the prevalence of ADHD change according to the region where the survey was conducted, analytical and collected. Barkley and Murphy (2008) estimate that the disorder reaches 3% - 7% of school-age children. Holmes et al. (2002) argue that this rate is actually 10%. Brazelton and Sparrow (2003) present another estimation, that the disorder affects 5% of school-age children. Regarding this diversity of results, Golfeto and Barbosa (2003) informs that differences in epidemiological data can vary from 1% to 20%, requiring a careful analysis of the studies. This is corroborated with the studies contained in Table 1, where one can observe a great disparity between the data on the prevalence of ADHD, ranging from 0.04% in the study of Aragonès et al. (2010) to 24.5% in Azevedo, Caixeta, Andrade and Bordin (2010) .

The assessment for the diagnosis of ADHD has been the key point for the design of epidemiological profile of the disorder (Barkley & Murphy, 2008; Vasconcelos et al., 2003; Pastura, Mattos, & Araújo, 2007) . Three main aspects affect the quality of these finds: 1) ADHD Definition; 2) Respondent and 3) Instruments used to collect the results.

On this behalf Andrade and Flores-Mendoza (2010) state:

Although it is a recurrent disorder with personal and social negative consequences, its epidemiological research and determination are searched by means of various evaluation methods and informants, which does not provide precise data on its prevalence in the general population. (p. 17)

ADHD is frequently confused with other developmental disorders, episodic diseases, and behavior problems without any organic component or environmental situations, such as home education without objective rules (Andrade & Flores-Mendoza, 2010; Cardoso, Sabbag, & Beltrame, 2007) . It is necessary to

consider also cultural patterns that interfere significantly in establishment of pattern behaviors that are considered appropriate and inappropriate in a specific reunion.

Montiel-Nava, Peña-Barbera and Montiel (2003) discuss this issue as follows:

In recent decades, changes in psychiatric nosology systems on the conceptualization of the disease, which affected the number and the combination of signals required for the diagnosis of ADHD. These changes contribute greatly to the disparity in prevalence rates reported in several studies. Other factors are related to the methods used, type of sample studied (clinical or community), the source of communication (parents, teachers, children), and sociocultural characteristics. Culture is one of the most powerful influencers in the normal development of a child or the occurrence of psychopathological variables, such as expectations and standards associated with adequate performance and children that vary from country to country behaviors. (p. 815)

The quality of information is directly related to the source. That means, depending on the level of relationship between those responding to the protocols and participants (with ADHD) behavior can be observed under different analyzes. The level of understanding of the respondent on the ADHD phenomenon is an important matter to discuss. Moreover, the validity of the instruments used to collect information plays decisive role for the establishment of epidemiological data (Molinero, Villalobos, Redondo, Martín Rivera, & Sanz, 2009; Montiel- Nava, Peña, & Montiel-Barbero, 2003) .

Studies of this nature that use procedures of in their own scales in detriment of the diagnostic criteria of DSM IV they avoid to discuss and to analyze critically consistent characteristics with ADHD in a range of situations that can assign or delete the final diagnosis. It is necessary to consider the age of simptomatological onset, frequency, damaged areas and levels of prejudice. It is this set of information that will ensure greater reliability to the results. In most studies, it is observed that these variables are not considered, and assigned a diagnosis of ADHD to all those who filled out a number compatible with the 1st criteria of DSM IV symptoms, without considering the other. Thus, multidimensional investigation is abandoned.

Molinero et al. (2009) state that:

The variability in prevalence figures is influenced by the determination of the sample, clinical and/or psychometric strategy, the cut used in the scales, the informant, age, origin, geographical location, diagnostic criteria and whether or not the proper definition of dysfunction. All this suggests that the comparison of the values obtained in different studies is not straightforward and should be done carefully because we are aware that the use of older samples, include measures of impairment or use two instead of one informant tend to offer a lower prevalence, while use against DSM-IV and DSM-IIIR criteria ICD-10 improves prevalence. (p. 253)

Although the criteria for diagnostic assessment of ADHD is increasingly standardized based on DSM IV. Some researchers have extrapolated the use of a single checklist to ensure the highest reliability of the data obtained. As observed in studies of Graaf et al. (2008) , Kessler et al. (2006) , Londoño, Cifuentes and Lubert (2011) , Molinero et al. (2009) , Montiel-Nava, Montiel-Barbero and Peña (2007) , Montiel-Nava, Peña and Montiel-Barbero (2003) , Pineda, Lopera, Henao, and Palacio Castellanos (2001) , Scandar (2003) and Vasconcelos et al. (2003) .

In general, we can arrange the instruments used in data collection in three main groups:

Behavioral Rating Scales: Checklists compounds of descriptive items of topography and frequency of behaviors. Likerts scales have been widely used for initial screening of repertoires consistent with the clinical picture of ADHD. These scales were developed with the primary basis of the diagnostic criteria of DSM IV and are usually applied in the form of interviews with parents and teachers. The adoption of instruments based on DSM IV strengthens the predictive quality and reliability of the data obtained, considering that these scales are based on observation of pattern behaviors, as well as the reports of others about the development of the person assessed. Among the articles that make up this work identified themselves quite often the scales (Table 2).

Neuropsychological Assessment Scales: Neuropsychological assessment is the use of tests to assess the level of cognitive development, as well as identify possible (functinal) areas affected by ADHD. In the studies reviewed here, the scales were used (Table 3).

Clinical Interview: The medical protocols have been important in identifying the developmental pathway of the subject. Thus, it is possible to exclude episodic diseases of atypical developmental conditions that have chronic nature, such as ADHD. In general, care services or health research groups in which the designs have been developed own history, which, unlike the scales for behavioral and neuropsychological assessment, do not go through the process of validation protocols. Some clinical routes used are listed in Table 4.