What the research found, and where it is small

Penttila M, Jaaskelainen E, Hirvonen N, Isohanni M, Miettunen J (2014). Duration of untreated psychosis as predictor of long-term outcome in schizophrenia: systematic review and meta-analysis. British Journal of Psychiatry, 205(2), 88 to 94 doi

Thirty three samples, pulled from an initial search of nearly three and a half thousand publications. A longer time without treatment was linked to a worse outcome later, across symptoms, the chance of remission, and social and general functioning. The size of that link was small, with correlations between 0.13 and 0.18, though it pointed the same way consistently. The authors also report, and this belongs next to the rest, that a longer wait was not significantly linked to employment, to quality of life, or to how many hospital admissions a person had.

Lim A, Hoek HW, Blom JD (2015). The attribution of psychotic symptoms to jinn in Islamic patients. Transcultural Psychiatry, 52(1), 18 to 32 doi

A review of 105 texts. Among the published case reports, most carried a definite medical diagnosis, and the largest group of those sat in the schizophrenia spectrum. The authors conclude that attributing symptoms to jinn is common among Muslim patients and has a real effect on diagnosis, treatment and course. Their own limit, and it is a serious one: published case reports are a selected sample, so this cannot tell you how common the attribution is in any population. No honest percentage exists for that, so none is printed here.