Table 3.

Agreement statistics (adapted from reference ²⁴).

		Method B
		Grade 1	Grade 2
Method A	Grade 1	a	b
	Grade 2	c	d

Raw agreement = (a+d)/(a+b+c+d)

Kappa = (observed agreement – expected agreement)/(1 – expected agreement)

where observed agreement = (a+d) / (a+b+c+d) and expected agreement = ((a+b)(a+c))/(a+b+c+d) + ((c+d)(b+d))/(a+b+c+d)

Odds Ratio (OR) = ad/bc

$$\mathrm{Phi}=\left(\left(\sqrt{\text{OR}}-1\right)/\left(\sqrt{\text{OR}}+1\right)\right)+\left(\left(\sqrt{\mathrm{a}\mathrm{b}}-\sqrt{\mathrm{b}\mathrm{c}}\right)/\left(\sqrt{\mathrm{a}\mathrm{d}}+\sqrt{\mathrm{b}\mathrm{c}}\right)\right)$$