The ranef statement specifies zero or more random effect parameters and their covariance structure. There can be more than one such statement in a model.
1 ranef(eta1
2 eta2=6
3 diag(eta3, eta4)
4 diag(eta5, eta6)=c(2, 3,)
5 same(eta7, eta8)
6 block(eta9, eta10)
7 block(eta11, eta12)=c(1, 0.2, 3)
8 block(eta13, eta14)(freeze)=c(1, 0.2, 3)
9 )
Line 1 says eta1 is a random effect that is independent of the other random effects. The initial estimate of its variance is one. (Note that, when the initial value is not provided, the PML uses a default value of one.)
Line 2 says eta2 is independent of the other random effects and that the initial estimate of its variance is six.
Line 3 says eta3 and eta4 have a diagonal variance-covariance matrix. The initial estimates of the diagonal elements for the variance-covariance matrix are one, the default.
Line 4 is like line 3, except that the initial values for the diagonal elements of the variance-covariance matrix are given by 2 and 3, respectively, where the function c is used to specify a list of numbers, similar to the R usage.
Line 5 says that eta7 and eta8 have the same diagonal variance-covariance matrix as eta5 and eta6 in line 4. Also, the covariance matrix is constrained to be the same as in the previous block. The random effects are different but drawn from the same distribution as those specified on line 4.
Line 6 says that eta9 and eta10 have a full variance-covariance matrix. The initial estimates for the diagonal elements of the variance-covariance matrix are one, while the estimates for the off-diagonal elements are zero, the default.
Line 7 is like line 6 and gives an initial estimate of the lower triangle of the matrix in row-wise order, that is, the initial values for the diagonal elements of the matrix are given by 1 and 3, respectively, while the off-diagonal element is 0.2.
Line 8 is like line 7 except that the matrix is fixed and is not estimated.
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