An array, matrix, or vector of importance ratios on the log scale (for PSIS-LOO these are negative log-likelihood values). See the Methods (by class) section below for a detailed description of how to specify the inputs for each method.

The importance sampling method to use. The following methods are implemented:

• "psis": Pareto-Smoothed Importance Sampling (PSIS). Default method.

• "tis": Truncated Importance Sampling (TIS) with truncation at sqrt(S), where S is the number of posterior draws.

• "sis": Standard Importance Sampling (SIS).

Arguments passed on to the various methods.