. 2011 May 9;173(11):1327–1335. doi: 10.1093/aje/kwr013

Appendix Table 1.

Notation used to demonstrate that the Pearson chi-squared statistic is equal to the risk reclassification statistic for the baseline risk model^a

	Category for Risk(Y)
	1	2	. . .	K	Total
Events	O₁	O₂	. . .	O_K	O = ∑O_k
Nonevents	n₁ − O₁	n₂ − O₂	. . .	n_K − O_K	n − ∑O_k
No. of subjects	n₁	n₂	. . .	n_K	n = ∑n_k
Event rate	$p_{1} = \frac{O_{1}}{n_{1}}$	$p_{2} = \frac{O_{2}}{n_{2}}$	. . .	$p_{K} = \frac{O_{K}}{n_{K}}$	$p = \frac{Σ O_{k}}{n}$

The upper 2 rows show notation corresponding to the Pearson chi-squared statistic. The lower 2 rows show notation corresponding to the risk reclassification statistic. There is only 1 category for the baseline risk.