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Table 1 Main characteristics of studies of prodromes and risk syndromes

From: Prodrome or risk syndrome: what’s in a name?

  Prodrome studies Risk studies
Primary focus Symptoms and signs preceding any episode onset for a specified disorder Predictive validity of ‘risk markers’ for 1st episode onset (versus no disorder or versus a different disorder)
Design Retrospective Prospective
Outcome New episode of a specified disorder Several possible outcomes (i.e. agnostic): presence or absence of disorder(s)
Reliability (+ positive; − negative) + High for late prodrome
− Boundary between final phase of a prodrome difficult to differentiate from episode onset
+ High levels for most features
− Less for some factors
e.g. reporting of family history of mental disorders affected by lack of information or recall biases
e.g. potential confounding of trait measures with prodromal symptoms
Statistical analysis Within group comparisons only (100% of the sample = Cases) Between group analyses: Cases vs. Controls
Limitations Sampling biases
Recall and response biases
Lack of generalizability to studies of risk markers
Operationalization of risk syndromes and methods for measuring any specific criteria are not standardized
In bipolar disorders, there is a lack of consensus regarding the goal, i.e. risk of onset of mania or of hypomania and mania (or of mixed states or affective psychosis)
High resource use and costly (due to e.g. sample size requirements and/or duration of follow-up)
Advantages Benefits for individuals can be instigated in the short-term (e.g. introduction of individualized relapse prevention programmes focused on early warning signs and symptoms)
Inexpensive; relatively easy to plan and undertake
Can estimate likelihood of onset of a range of disorders in individuals and populations that have similar or different levels of risk
Opportunities for use of enriched strategies (e.g. offspring studies)
Identification of putative protective factors and/or exploration of interactions between risk and protective factors will inform prevention and early intervention strategies