NEWS.md

In MultiSpline: Spline-Based Nonlinear Modeling for Multilevel and Longitudinal Data

MultiSpline 0.2.0

Major new features

• Two-way and nested clustering via cluster = c("g1","g2") and nested = TRUE/FALSE, generating (1|g1/g2) or (1|g1) + (1|g2) random-effects structures in lme4.

• Automatic knot / df selection (df = "auto" in nl_fit() or via nl_knots()) using AIC or BIC over a user-specified grid.

• Multilevel R-squared decomposition (nl_r2()): Nakagawa-Schielzeth marginal R2m and conditional R2c, plus a level-specific variance partition table (r2_mlm style) for LMM, GLMM, and single-level OLS / GAM models.

• Full postestimation suite:

• nl_derivatives() — first and second derivatives with delta-method confidence bands.
• nl_turning_points() — local maxima, minima, inflection regions, and slope-direction regions.

• nl_plot() gains type = "slope", "curvature", and "combo" in addition to the original "trajectory".

• Built-in model comparison workflow (nl_compare()): contrasts linear, polynomial, and spline fits by AIC, BIC, log-likelihood, and likelihood-ratio tests.

• B-spline basis (method = "bs", bs_degree argument).

• Random spline slopes (random_slope = TRUE) to allow the nonlinear effect to vary across clusters.

• Cluster heterogeneity analysis (nl_het()): plots cluster-specific trajectories (BLUPs) and performs an LRT comparing random-slope vs random-intercept models.

• CI for glmerMod: approximate confidence intervals via the delta method on the link scale (default, fast) or parametric bootstrap (glmer_ci = "boot").

Breaking changes

None. All v0.1.0 calls remain valid.

Bug fixes

• nl_r2() variance partition now correctly excludes NA entries that could appear when lme4 internal row names are ambiguous in nested models.
• nl_predict() now correctly computes CI when control variables are stored as character (not factor) in the original data.
• nl_plot() no longer errors when time = NULL and the data frame has no time column.

Dependency changes

• %||% is now imported from rlang rather than defined internally, avoiding namespace masking.
• reformulas moved from Imports to Suggests (used opportunistically for nobars(); falls back to lme4::nobars() if unavailable).

MultiSpline 0.1.0

• Initial release: nl_fit(), nl_predict(), nl_plot(), nl_summary(), nl_icc().

MultiSpline documentation built on April 16, 2026, 9:06 a.m.