Environmental Health

Table 6 Notation for a general two-by-two table

From: Bias magnification in ecologic studies: a methodological investigation

	exposed	unexposed	sum
cases	p _i m _{i 1}	q _i m _{i 0}	p _i m _{i 1}+q _i m _{i 0}
noncases	(1-p _i)m _{i 1}	(1-q _i)m _{i 0}	(1-p _i)m _{i 1}+ (1-q _i)m _{i 0}
total	m _{i 1}	m _{i 0}	n _i= m _{i 1}+m _{i 0}
risks	p _i	q _i
RD	p _i-q _i
X _i			m _{i 1} /n _i
Y _i			(p _i m _{i 1}+q _i m _{i 0})/n _i

Let p _iand q _ibe the risks of the exposed and unexposed in group i. Let m _{i 1}and m _{i 0}be the numbers of exposed and unexposed in group i. RD = risk difference; X _iand Y _iare the average exposure and average risk in group i; n _i= size of group i.

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ISSN: 1476-069X

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