Critical period in early psychosis intervention: possible dose effect from longitudinal studies from Hong Kong

Abstract

Purpose: The critical period hypothesis – that the outcome of psychosis is largely determined within the first few years — constitutes a rationale for focusing psychosis intervention resources on the early years. This hypothesis predicts that intervention in the initial years yields better outcomes that are maintained in the subsequent post-intervention years. Since 2001, Hong Kong has provided two years of specialised early service to patients with first-episode psychosis aged 15 to 25. Controlled studies suggest that this yielded improved outcomes that were sustained for up to 10 years. This suggests an overall efficacy of intervention consistent with the critical period hypothesis. We further explored enhancing the intervention with an additional year of service. Method: Patients completing two years of intervention were randomised to receive either one more year of intervention (three years total), or to transition to a year of standard care. Results: The functioning of patients receiving an additional year of intervention continued to improve in the third year, while that of the control group remained unchanged. However, the effects of this additional year did not persist, largely due to catch-up in the group which did not receive additional intervention. Conclusion: We conclude that after two years, further outcome improvements could be effected. Our observations are suggestive of a dose effect of intervention. The critical period effect is evident with lower-level input, but with more input, the additional benefit did not persist. The validity of the critical period hypothesis is not uniform and appears contingent upon the intensity of intervention.