TABLE 1.

Maximum-likelihood test for the molecular clock hypothesis^a

Data set	Log likelihood		2(In ML − In MLK)	χ2 (0.95)	Statistical significance level (P)	Rejection of the molecular clock hypothesis
	ML	MLK
LTR	−1,968.13	−2,727.04	1,517.81	23	0.001	No
env	−7,334.43	−10,017.67	5,366.47	35	0.001	No

^aCalculation of the statistical significance of rejecting the molecular clock hypothesis using the χ² test comparing maximum likelihood and maximum likelihood with enforced molecular clock. The hypothesis that PERV does evolve according to a molecular clock is rejected, if the significance p is larger than 0.05. ML, maximum likelihood method; MLK, likelihood method enforcing a molecular clock using the ML topology. The calculation was performed using the software package DAMBE (44) according to the instructions given in reference 39.