Under a pure birth model, this statistic follows a normal distribution with mean = 0 and standard deviation = 1.
The exploratory data analysis tool, tree deviation, was devised to detect trees that, on average throughout their history, have had a greater number of lineages than expected under a pure birth model (at α = 0.05).
According to Zhou and Hethcote [9], when (a=1), (1) could be called a logistic birth model, and when (a=0), (1) could be called a logistic death model.
One commonly used method to detect deviations from a pure birth model is the constant-rates test proposed by Pybus and Harvey [7], often referred to simply by its test statistic, γ (equation 1 in [7]).
We first applied a "pure birth" model (constant transposition rate and no deletion) (table 1).
The date for node 35 was interpolated according to a constant birth model (see Methods).
Using a nonhomogeneous birth model (21), we investigated the association between subtype H5N1 presence in infected poultry flocks and wild birds.
A pure birth model (Yule) was assigned as prior for the branching process and two independent and identical runs were conducted for each BEAST setup for 306 generations.
The simplest model involves only birth events with a constant rate (using the notation presented in the previous section, and ), which describes a "pure birth" model or Yule process (after Yule 1924).
Statistical analyses of the LTT plot for brachinines indicated that a Pure Birth model of constant rate of diversification (Model 1, AIC = 54.42) could not be rejected (Table 5).
