PoC: move regression tables to modelsummary (msummary_r helper + ch13 Table 13.2)

[gbekes]

Goal

Proof of concept for standardizing the repo's R regression tables on modelsummary instead of stargazer/stargazer_r. Scoped to one chapter (ch13) plus a reusable helper, so the numbers and ergonomics can be reviewed before a full sweep.

What's here

1. msummary_r() in ch00-tech-prep/da_helper_functions.R — a modelsummary-based counterpart to stargazer_r(), same interface:
   • se = 'robust' (HC1) / 'traditional' / 'newey-west' (max_lag)
   • gof = which fit stats to keep (mirrors keep.stat); default n + rsq
   • fmt / stars / output / title / ... pass through to modelsummary()
2. ch13 Table 13.2 (multireg1, linear models 1–4) now built with msummary_r().

Why the numbers are safe

Robust SE = vcovHC(type="HC1") — exactly what stargazer_r() / calculate_se() already compute, and the same as fixest vcov='hetero'. I verified msummary_r's HC1 SEs against the old stargazer_r SEs:

model 1:  3 coefs, max diff = 0.0e+00
model 2:  4 coefs, max diff = 0.0e+00
model 3:  9 coefs, max diff = 0.0e+00
model 4: 13 coefs, max diff = 0.0e+00

Table reproduces N = 281 and R² 0.847 → 0.898 → 0.913 → 0.919.

Two things to decide for the book build

• LaTeX backend. .tex renders via modelsummary's default tinytable backend, which needs a tabularray preamble. If the book's build expects booktabs/longtable (as stargazer emitted), switch the output to the kableExtra backend. This is the one house-style call before a full migration.
• Text output. .txt is now a grid/markdown table rather than stargazer's plain ASCII (cosmetic).

Scope notes

• Deliberately one chapter. Non-model frames (the CV matrix and prediction summaries in ch13) are left on stargazer/kable — modelsummary isn't the right tool for those.
• Descriptive tables across the repo already use datasummary (modelsummary family), so the remaining work for a universal R move is mainly the regression tables.
• Stacked on fix-ch13-fct-explicit-na (PR Fix deprecated fct_explicit_na() in ch13 used-cars script #146) so ch13 runs end to end. Merge that first, or this PR will retarget to master automatically.

🤖 Generated with Claude Code