TABLE 4.

Expected number of avian B-allele introductions

Data	A allele			B allele			Fisher testa
	No. of avian virus strains	No. of independent introductions	Introduction rate	No. of avian virus strains	No. of independent introductions	Introduction rate	P value	Expected no. of B-allele introductionsb
All avian viruses	9,617	32	0.0033	2,717	6	0.0022	0.436	9.04 (4–15)
Transmissible viruses	9,617	19	0.0020	2,717	3	0.0011	0.446	5.37 (0–10)
Single isolates or viruses with poor transmission	9,617	13	0.0014	2,717	3	0.0011	1.000	3.67 (0–8)
Viruses from domestic birds only	4,391	18	0.0041	648	3	0.0046	0.756	2.66 (0–6)
Viruses from wild birds only	5,168	12	0.0023	2,053	3	0.0015	0.578	4.77 (1–9)

^aCalculated using data from A alleles, assuming a binomial distribution.

^bData in parentheses represent the range of the number of episodes that would still be statistically nonsignificant (P ≥ 0.1).