Almost one in eight young people are in youth services (e.g. mental health services). Abnormal development refers to development not being normal and often includes excessive parts of behaviour or behaviour that is not shown enough. Cognitive distortions are common. There are several definitions:

• Absence of disorders
  This is limited as this does not allow for treatment of a problem when it does not classify as a disorder.
• Statistical fact (i.e. what the majority of the people do is ‘normal’).
  This includes a deviation from the mean and is based on standard deviations. One limit is that it is arbitrary where the cut-off of the norm is.
• Desired or ideal state
  This views normality as a desired or ideal state. It relies on considerations of what is normal (e.g. Erikson’s theory of psychosocial development).
• Successful adaptation
  This views normality as a successful adaptation to the environment, meaning that normality depends on the context and not necessarily on the behaviour.

Classification is important as it gives directions to what is normal and what is abnormal. It contains a meaningful grouping of symptoms and syndromes. It is important to have knowledge of what is normal to determine when there is a problem and when there is a disorder. There are two levels of classification:

1. Mode of functioning
   This includes determining whether functioning is abnormal, deviant and/or in need of treatment.
2. Mode of distinguishing
   This includes distinguishing among different dimensions or types of psychological functioning

There are two main functions of classification systems:

1. Communication
   It allows for better communication among professionals as it defines the rules by which psychological constructs are defined.
2. Documentation of need for services
   It allows for the documentation of need for services (e.g. whether a child is eligible for special education services).

There are several advantages of using a classification system such as the DSM-V:

• It facilitates clear communication between youth care parties.
• Classification refers to clinically relevant types (i.e. syndromes).
• Classification provides access to money or specialized care (i.e. insurance).
• A label promotes acceptance of children with learning and behavioural problems.

There are also several disadvantages of using the DSM-V:

• Classification systems attempt to fit people into arbitrary categories even though there may not be a perfect fit (i.e. loss of information).
• Classification systems give the idea that there is a clear-cut difference between normal and abnormal.
• Classification systems can stigmatize patients (e.g. schizophrenics).
• There are often no age-related criteria.
• The label can be used as an excuse to not treat the disorder.
• The DSM-V can lead to overreporting as it provides access to treatment.
• It focuses on child characteristics rather than the environment.

There are several theoretical models on which a classification system can be based:

1. Medical model (i.e. latent variable model)
   This model holds that there is a core deficit (i.e. latent variable) and there are symptoms that define the presence of the disorder. There is a sharp distinction between normal and abnormal and the disorders differ depending on the theories used to define the deficit.
2. Multivariate approach (i.e. empirically-based approach)
   This model holds that there are interrelated patterns (i.e. syndromes) of behaviour defined by statistical relationships between behaviours. It does not hold that there is a core of the disorder (i.e. network model) and states that a disorder is a continuum.

The four-factor model states that a child’s problem behaviour is influenced by:

• Parent factors.
• Environmental factors.
• Child factors.
• Education factors (e.g. parenting).

There are also several protective factors:

• Parent factors (e.g. stable relationship)
• Child factors (e.g. strengths)
• Environment (e.g. quiet neighbourhood)
• Education factors (e.g. skills).

There are some isolated behaviours that are reported by less than 5% of the parents of 4 to 18-year-olds and could be indicative of a disorder:

• Compulsory behaviour.
• Running away from home.
• Threatening others.
• Seeing things that are not there.
• Skipping class (up to 14).
• Use of alcohol or drugs (up to 15)
• Arsonage (in girls)
• Playing with stool.
• Vandalism (boys up to 14).
• Wetting pants (after 7)
• Suicide attempts.
• Desire to be of the opposite sex (in boys)

The WISC-V and the SON are IQ-tests that rely on the statistical definition of normal and abnormal behaviour. There are several categorizations of problems:

• Externalizing problems (e.g. ADHD)
• Internalizing problems (e.g. depression).
• Substance abuse (e.g. alcohol)
• Learning disability or intellectual disability (e.g. dyslexia)
• Severe psychopathology (e.g. schizophrenia)