Risk factors - criteria
	n Three criteria need to be satisfied in order to identify a characteristic as a risk factor: 1.  the factor must be observed to covary with the disease •  i.e., the factor must be statistically associated with the development of the disease • or equivalently, the frequency of disease must be observed to differ by category or value of the factor 2.  the presence of the risk factor ( or a relevant change in the risk factor) must precede occurrence of the disease
		ohcd603			18