Psychopathology
Psychopathology: Reliability and validity in diagnosis and classification of disorders
Aim
The aim of this worksheet is to improve your critical evaluation skills and understanding of the terms ‘reliability’ and ‘validity’. The exam for this topic will test not only your knowledge of classification systems, but also your understanding of the research that has critically evaluated such systems and the issues of reliability and validity and their implications that have resulted.
Answer the following questions. Remember that marks in the examination are awarded for how ‘effective’ your evaluation is, as well as how accurate.
Questions
1 Write down a definition of the term ‘reliability’ and a definition of the term ‘validity’. Make sure that you understand the difference between the two.
2 What classifications systems are there, and what are the clinical characteristics that they give for your chosen disorder? What are their similarities and differences? Make a list of clinical characteristics that classifications have in common, and a list of where they differ. Clinical characteristics that always appear in all systems can be said to be reliable because of this consistency.
3 Are the classification systems consistent over time? Are there any differences, for example, between different versions of the DSM or ICD?
4 Would clinicians always agree on a diagnosis for a given individual? For example, how much difference is there really between delusions of grandeur associated with bipolar disorder and schizophrenia, or an unwillingness to leave one’s home due to depression, social phobia or a checking compulsion. A lack of agreement would suggest poor inter-rater reliability, and you should consider the implications for the validity of diagnostic criteria too. An inability among experts to agree would indicate a problem with validity.
5 Do diagnoses remain constant over time, that is, would a diagnosis for an individual be changed at all after having been made? What are the consequences for reliability and validity?
6 Are classification systems reliable between cultures, that is, are clinicians in different parts of the world applying the same criteria in the same way?
Even if the answer to the last four questions was ‘yes’, this would merely indicate reliability, not validity. A lack of reliability always causes us to question validity, in this case, that the systems may not be accurate because classification systems and the research they are based on disagree. However, the reverse is not true. Just because classification systems agree, that does not mean they are truthful and accurate since it is possible that they are all wrong. For example, there was once a reliable consensus that the world was flat, which was inaccurate. Two types of validity that you can consider are descriptive and predictive validity.
7 Do classification systems for your chosen disorder have descriptive validity, that is, can they describe syndromes accurately and differentiate between different categories? You could look at co-morbidity here as well as reliability.
8 Do they have predictive validity, or the ability to predict the course of the disorder and the efficacy of any treatments?
9 Are there any other objections to the validity of classification systems? Is the concept of ‘mental illness’ valid or is there a better way of distinguishing between ‘normal’ and ‘abnormal’ thoughts, feelings, and behaviour? Is the research that the systems are based on valid?
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