Use simple linear regression to find the initial value of betas in free approach, where beta are the effects/coefficients for the count model.
regression(y, x)The response vector.
The design matrix (n by p, p is the number of covariates) for the count model (e.g., beta-binomial), and intercept is included.
Initial values for beta estimation matrix (p by m, p is the number of involved covariates and m is the number of OTUs).
Standard errors for the estimated betas.