Exercise 18 D.2 Null Hypothesis, H 0 : There is a relationship between smoking marijuana as a teenager and suffering schizophrenia within the next 15 years. Alternative Hypothesis, H 1 : There is no relationship between smoking marijuana as a teenager and suffering schizophrenia within the next 15 years.

Observed Value Table SchizophreniaNon-SchizophreniaTotal Smokers Non-smokers Total Expected Value Table SchizophreniaNon-SchizophreniaTotal Smokers(131 x 327)/1024 = 41.8(131 x 697) / 1024 = Non-smokers893 x 3270 / 1024 = 285.2(893 x 697) / 1024 = Total If the variables are independent, expected value = product of probability each variable x total number of values e.g. P(smokers and schizophrenia) = P(smoker) x P(schizophrenia) x 1024 = (131/1024) x (327/1024) x 1024 = (131x 327)/1024 = 41.8

Calculating X 2 (chi-squared) X 2 =∑ (f o - f e ) 2 f e fofo fefe f o - f e (f o - f e ) 2 f e , Total10.57 X 2 = 10.57

df = (r – 1) (c – 1) = (2 – 1) (2 – 1) = 1 Significance level = 5% = 0.05 Reject hypothesis if X 2 calc > 3.84, > 3.84 so reject hypothesis. It therefore suggests that there is no relationship between smoking marijuana as a teenager and suffering schizophrenia within the next 15 years.