rstanarm v2.21.3

Bug fixes

• Fix bug where loo() with k_threshold argument specified would error if the model formula was a string instead of a formula object. (#454)

• Fix bug where loo() with k_threshold argument specified would error for
  models fit with stan_polr(). (#450)

• Fix bug where stan_aov() would use the wrong singular.ok logic. (#448)

• Fix bug where contrasts info was dropped when subsetting the model matrix in
  stan_glm(). (#459)

• Fix bug where stan_glmer() would error if prior_aux=NULL. (#482)

• posterior_predict() and posterior_epred() don't error with newdata for
  intercept only models by allowing data frames with 0 columns and multiple rows. (#492)

New features

• New vignette on AB testing. (#409)

• stan_jm() gains an offset term for the longitudinal submodel. (#415, @pamelanluna)

• Effective number of parameters are computed for K-fold CV not just LOO CV. (#462)

• stan_clogit() now allows outcome variable to be a factor. (#520)