MethodIn the development of complex nursing interventions, a careful procedure should be followed. []have designed a model for the development of evidence-based nursinginterventions. The essence of this model is that a number of steps haveto be followed for the intervention development that have the objectiveof providing the building blocks for the design of the intervention.These building blocks can be assembled by means of the literature, analysis of the problem for which the intervention is intended, research into the needs of patients and the social system and theresulting demand for care, and research into already existingintervention practices. The review of the literature is an obligatorycomponent of the process of intervention development. The use of theother research possibilities depends on the state of the knowledge andthe concrete research opportunities within the intervention areaconcerned.The following two studies preceded the intervention development described in this article: a review of the literature [];and a qualitative study of present intervention practices of earlyrecognition and early intervention in The Netherlands [ and ].This study provides an understanding of various methods and proceduresthat are presently already applied. It also offers insight into theexperiences and needs of patients, family members, and care providerswith these methods. The results of these substudies constitute thebasis for an initial design of the intervention protocol. This designwas presented to eight experts in the area of schizophrenia care: twopsychiatric nurses, two psychiatrists, two clinical psychologists, andtwo family members of schizophrenic patients. They studied the protocoland participated in a semistructured interview. Their judgments led tofurther adaptation of the protocol.The protocol was then testedin nursing practice. Four nurses who work in a teaching hospital andwho have expert knowledge in the field of the care of patients withschizophrenia received instructions on the background and applicationof the protocol. Then, they applied the protocol with six patients. Thefirst author also applied the protocol with two patients. Patientselection was done by purposive sampling to have variation of thepatient characteristics regarding sex, age, illness duration, treatmentsetting clinic, day clinic, outpatient treatment, severity ofsymptoms, and level of social functioning. The nurses kept a log inwhich they noted their experiences, questions, and comments. The firstauthor was available as a consultant for coaching the nurses while theprotocol was being applied.During the implementation of theprotocol, the nurses were interviewed at the following two times: halfway through the implementation of the protocol, that is, after theinventorying of early warning signs; and after the protocol wascompleted in its entirety, ie, when all the relevant data for thepatient and the family were entered in a symptom recognition plan. Theresults of the case studies were used to improve the protocol.First,we briefly discuss the theoretical model that underlies theintervention. Second we present the structure and the procedure of theprotocol; and third, we summarize the judgments of the experts anddescribe a number of experiences from the case studies.The theoretical model: the vulnerability-stress modelThevulnerability-stress model is a tentative model for treatment andresearch in the field of schizophrenia and related disorders. The modelattempts to integrate the available state-of-the-art knowledge in thefield of schizophrenia into a holistic perspective in which bothbiological and psychosocial variables have a place [ and ].The model see shows that the interaction of enduring personal vulnerabilityfactors, personal protectors, environmental protectors, and environmental potentiators and stressors lead to â??intermediate internalstates.â? Information-processing overload, tonic autonomichyperactivitation, and deficient processing of social stimulicharacterize the condition of the patient. These intermediate statescan, when they exceed a certain threshold of gravity, lead to thedevelopment of â??prodromal symptoms.â? They can be the precursors of apsychotic relapse. The feedback loops reflect the circularity of themodel. KFig.. The vulnerability-stress-model. Reprinted with permission from []. The model is excellently suited for the development of psychosocial interventions []because it makes the variables visible on which these interventions canbe carried out. In the description of the intervention, we refer tothis model.