svrep 0.5.0

• This release adds extensive new functionality for two-phase designs. The new vignette "Replication Methods for Two-phase Sampling" describes the new functionality as well as the underlying statistical methods.

  • The function as_gen_boot_design() can now create generalized bootstrap weights
    for two-phase survey design objects created with the 'survey' package's twophase() function.
    The user must specify a list of two variance estimators to use for each phase, e.g. list('Stratified Multistage SRS', 'Ultimate Cluster').

  • The function make_twophase_quad_form() can be used to create a quadratic form
    for a two-phase variance estimator, by combining quadratic forms from each phase.

  • The helper function get_nearest_psd_matrix() can be used to approximate
    a quadratic form matrix by the nearest positive semidefinite matrix. This can be
    particularly useful for two-phase designs, since the double
    expansion estimator commonly used in practice frequently does not have a
    variance estimator which is positive semidefinite.

• The function as_gen_boot_design() has a new argument named psd_option, which
  controls what will happen if the target variance estimator
  has a quadratic form matrix which is not positive semi-definite.
  This can occasionally happen, particularly for two-phase designs. By default,
  the function will warn the user if the quadratic form is not positive semi-definite
  and then automatically approximate the matrix by the nearest positive semi-definite matrix.

• Added a new function get_design_quad_form(),
  which determines the quadratic form matrix of a specified variance estimator,
  by parsing the information stored in a survey design object created using the 'survey' package.

• Added a new function rescale_reps() which implements the rescaling of replicate
  adjustment factors to avoid negative replicate weights. This functionality
  already existed in as_gen_boot_design() and make_gen_boot_factors(), but now
  it is implemented with the help of this new function.

• Added helper function is_psd_matrix() for checking whether a matrix is positive semi-definite,
  and added a helper function get_nearest_psd_matrix() for approximating a square matrix
  by the nearest positive semi-definite matrix.

• Minor improvements to vignettes, particularly formatting.