Neurodevelopmental disorders are different from adult acquired disorders involving traumatic brain injury because they involve no period of normal development. Any IQ score in a neurodevelopmental disorder is confounded with the condition. The IQ score can never be separated from the effects of the condition.

Early on in intelligence testing, IQ was seen as a latent

There are three important questions when assessing the relationship between variables:

1. Statistical significance
2. Effect size
3. Practical significance

The practical significance (i.e. clinical significance) can be assessed by considering factors such as clinical benefit (1), cost (2) and side effects (3). In order to assess the practical significance, the strength of the association

Randomized controlled trials without sufficient statistical power may not adequately test the underlying hypotheses. This makes it useless and, thus, unethical. However, underpowered research continues to be conducted.

Arguments in favour of using underpowered research are that meta-analyses may save the small studies by providing a means of combining the results with those of similar studies (1)

The statistical crisis (i.e. replication crisis) refers to the fact that statistical significance does not necessarily provide a strong signal in favour of scientific claims.

One major challenge for researchers is accepting that one’s claims can be spurious. Mistakes in statistical analyses and interpretation should be accepted and learned from rather than resisted. Criticism and replication

Multilevel modelling (MLM) is becoming the standard for analysing nested data.

The unit of analysis problem refers to when the moderator variable exists at a different level than the independent and dependent variable (e.g. moderator variable is on the level of the course itself and the independent and dependent variables are on the individual level). Multilevel

In the advanced neuropsychological diagnostics infrastructure (ANDI), datasets of several research groups are combined into a single database. It contains scores of neuropsychological tests from healthy participants. This allows for accurate neuropsychological assessment as the quantity and the range of the data surpasses most traditional normative data. It facilitates normative comparison methods (e.g. those in which entire profiles

Evidence-based treatment refers to interventions or techniques that have therapeutic changes in controlled trials. Disadvantages are that key conditions and characteristics of treatment research are different from clinical practice and that research tends to focus on symptoms, rather than the patient as a whole. Determining whether a treatment is evidence-based or empirically supported has different criteria (1), makes

There are several ethical guidelines in science:

1. Always do an a-priori power analysis
   In underpowered studies, there might be insufficiently meaningful information (1), more replicability problems due to the higher probability of type-II errors (2) and are a waste of resources (3). In overpowered studies, it unnecessarily exposes participants to an intervention which may not

Nested data (i.e. multilevel data) refers to data gathered in multiple groups (e.g. intervention study in multiple classrooms). Nested data that is analysed in the usual way can have strong consequences for the significance of the results (i.e. results being significant while they are actually not). Nested data being analysed in the wrong way leads to drawing false

The advantages of analysing multiple individuals are that it allows for generalization of findings to others. However, it does not tell us anything about the individual. The analysis of an individual does not allow for generalization to others but does tell us something about the individual.

In an N=1 analysis, the baseline is compared with a treatment