A 23 year old engineering student is brought by his family to the hospital with a history of gradual onset of suspiciousness, muttering and smiling without clear reason, decreased socialization, violent outbursts, and lack of interest in studies for 8 months. Mental status examination revealed a blunt affect, thought broadcast, a relatively preserved cognition, impaired judgment and insight. He is most likely to be suffering from -
Delusional disorder
Depression
Schizophrenia
Anxiety disorder
This patient has:-


Delusions of control (thought broad casting)
Disorganized speech (muttering)
Disorganized behavior (smiling without clear reason, violent outbursts)
Negative symptoms (blunted affect, lack of interest, decreased socialization).
Duration of 8 months


Diagnostic criteria for schizophrenia:- Two or more of the following symptoms (each should be present for 1 month or more) and causing social or occupational dysfunction for 6 months or more.


Delusion  
Hallucinations
   Disorganized speech
Disorganized or catatonic behavior
Negative symptoms                                                                                                                                                                      
Only one of the above is required if delusions are bizarre or there are third person hallucinations.