Abstract
Background
Recent research on the negative symptoms of schizophrenia has produced reliable and validated scales such as the Scale for the Assessment of Negative Symptoms (SANS), the Schedule for the Deficit Syndrome, the Negative Symptoms Scale of Lewine, and others (1–3). More than 30 negative symptoms have been described, among these, avolition which is considered a core negative symptom (4). The DSM-5 recognizes five main negative symptoms: blunted affect, avolition, alogia, anhedonia and asociality (5). Other researchers consider attention impairment, poor self- care, and psychomotor retardation as negative symptoms (1, 6). There is a need to derive a short list of the core negative symptoms (CNS) of schizophrenia that are reliable and useful in clinical settings and clinical research.
Methods
The Standard for Clinicians’ Interview in Psychiatry (SCIP) is a new valid and reliable diagnostic interview that was tested in an international multisite study in three countries (USA, Canada and Egypt) between 2000 and 2012 (7–10). A total of 700 patients were interviewed at William R. Sharpe Jr. Hospital in Weston, West Virginia (670 patients) and Chestnut Ridge Center in Morgantown, West Virginia (30 patients). Mean patient age was 34, 59% male, 95% White and 34% had less than 12 years of education. The SCIP includes 8 items covering the main negative symptoms of schizophrenia: avolition, blunted affect, alogia, psychomotor retardation, poor self-care, anhedonia, attention impairment, and asociality.
Results
Inter-rater reliability Kappa (k) and standard error (SE) were calculated for each of the main negative symptoms: avolition (k=0.74, SE=0.04), blunted affect (k=0.68, SE=0.05), alogia (k=0.62, SE=0.05), psychomotor retardation (k=0.72, SE=0.04), poor self-care (k=0.79, SE=0.06), anhedonia (k=0.87, SE=0.04), attention impairment (k=0.92, SE=0.12), asociality (k=0.74, SE=0.04).
Cronbach’s alpha for internal consistency and the mean interitem correlation (MIC) of several models were calculated. Cronbach’s alpha and the MIC of the five-factor negative dimension (blunted affect, avolition, alogia, psychomotor retardation and poor self-care) were: alpha = 0.83, MIC=0.49. The item-rest correlations (IRCs) of each of the 5 negative symptoms were: blunted affect = 0.68, avolition = 0.57, alogia = 0.67, psychomotor retardation = 0.61 and poor self-care = 0.57. The high item-rest correlations of all five negative symptoms may indicate that they represent the Core Negative Symptoms (CNS) of schizophrenia.
Adding anhedonia to the five-factor model to create a six-factor model resulted in a low item-rest correlation (IRC) of anhedonia (IRC=0.06) and a lower alpha (0.76).
Similarly, adding attention impairment to the five-factor model to create a six-factor model resulted in a low item-rest correlation (IRC) of attention impairment (IRC=0.02) and a lower alpha (0.75). Similarly, adding asociality to the five-factor model to create a six-factor model resulted in a low item-rest correlation (IRC) of asociality (IRC=0.05) and a lower alpha (0.75). Finally, adding anhedonia, attention impairment and asociality to the five-factor model to create an eight-factor model resulted in low IRCs for anhedonia, attention impairment and asociality (IRCs are 0.12, 0.06, 0.10 respectively) and a lower alpha (0.67).
Discussion
The Core Negative Symptoms (CNS) Scale includes five negative items. Three items (avolition, psychomotor retardation and poor self-care) have good agreement (kappa >0.7) and two items (alogia and blunted affect) have fair agreement (kappa ranges from 0.5 to 0.7). Cronbach’s alpha was also high (0.83). The CNS scale can therefore be considered reliable at the dimensional level.
Avolition as the core negative symptom in schizophrenia: relevance to pharmacological treatment development