Table 1 Main characteristics of studies of prodromes and risk syndromes
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 |