# Model-based continuous summary tables in R

    library(spicy)

`table_continuous_lm()` is the model-based companion to `table_continuous()`. It fits one linear model per selected continuous outcome using `lm(outcome ~ by, ...)`, then returns a compact reporting table. This makes it the better choice when you want to stay in a linear-model workflow, add heteroskedasticity-consistent standard errors, or apply case weights.

## Basic usage

Use `select` for one or more continuous outcomes and `by` for the single predictor:

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi, life_sat_health),
      by = sex
    )
    #> Continuous outcomes by Sex
    #>
    #>  Variable                       │ M (Female)  M (Male)  Δ (Male - Female)
    #> ────────────────────────────────┼─────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100)  │   67.16      71.05          3.89
    #>  Body mass index                │   25.69      26.20          0.51
    #>  Satisfaction with health (1-5) │    3.51       3.59          0.08
    #>
    #>  Variable                       │ 95% CI LL  95% CI UL    p     R²    n
    #> ────────────────────────────────┼─────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100)  │    2.13      5.64     <.001  0.02  1200
    #>  Body mass index                │    0.09      0.93      .018  0.00  1188
    #>  Satisfaction with health (1-5) │   -0.06      0.22      .267  0.00  1192

For categorical predictors, the table reports estimated means by level. When the predictor is dichotomous, it can also show a single mean difference and confidence interval.

## Robust standard errors

Use `vcov = "HC*"` when you want heteroskedasticity-consistent standard errors and tests:

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = sex,
      vcov = "HC3",
      statistic = TRUE
    )
    #> Continuous outcomes by Sex
    #>
    #>  Variable                      │ M (Female)  M (Male)  Δ (Male - Female)
    #> ───────────────────────────────┼─────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │   67.16      71.05          3.89
    #>  Body mass index               │   25.69      26.20          0.51
    #>
    #>  Variable                      │ 95% CI LL  95% CI UL   t      p     R²    n
    #> ───────────────────────────────┼───────────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │   2.12       5.65     4.32  <.001  0.02  1200
    #>  Body mass index               │   0.09       0.93     2.38   .018  0.00  1188

The `HC*` family is computed via [sandwich::vcovHC()] and includes `"HC0"`, `"HC1"`, `"HC2"`, `"HC3"` (default for small / moderate samples), `"HC4"`, `"HC4m"`, and `"HC5"`.

## Cluster-robust standard errors

When observations are not independent (repeated measurements per individual, students nested in classes, panel data), classical and `HC*` standard errors are biased downward. Use the `CR*` family together with `cluster = id_var` to get cluster-robust inference, dispatched to `clubSandwich`:

    table_continuous_lm(
      sleep,
      select = extra,
      by = group,
      vcov = "CR2",
      cluster = ID,
      statistic = TRUE
    )
    #> Continuous outcomes by group
    #>
    #>  Variable │ M (1)  M (2)  Δ (2 - 1)  95% CI LL  95% CI UL  t(9)   p     R²   n
    #> ──────────┼─────────────────────────────────────────────────────────────────────
    #>  extra    │ 0.75   2.33     1.58       0.70       2.46     4.06  .003  0.16  20

`"CR2"` is the recommended default (Bell & McCaffrey 2002; Pustejovsky & Tipton 2018). It produces fractional Satterthwaite degrees of freedom, rendered in the displayed test header as e.g. `t(8.7)` or `F(2, 12.4)`. `"CR1"` matches Stata’s `vce(cluster id)` default.

## Bootstrap and jackknife

For situations where the residual distribution is non-standard or the sample is small, `vcov = "bootstrap"` and `vcov = "jackknife"` provide resampling-based variance estimators in pure base R (no dependency added):

    table_continuous_lm(
      sochealth,
      select = wellbeing_score,
      by = sex,
      vcov = "bootstrap",
      boot_n = 1000  # default
    )

When `cluster` is supplied, bootstrap switches to a cluster bootstrap (Cameron, Gelbach & Miller 2008) and jackknife to leave-one-cluster-out (Quenouille 1956). Both estimators use asymptotic inference: `z` for single-coefficient contrasts and `chi^2(q)` for the global Wald test on `k > 2` categorical predictors, rendered in the displayed test header.

## Case weights

Use `weights` when you want weighted estimated means or slopes in the same model-based table:

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = education,
      weights = weight,
      show_weighted_n = TRUE
    )
    #> Continuous outcomes by Highest education level
    #>
    #>  Variable                      │ M (Lower secondary)  M (Upper secondary)
    #> ───────────────────────────────┼──────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │        67.55                80.88
    #>  Body mass index               │        25.96                23.39
    #>
    #>  Variable                      │ M (Tertiary)    p     R²    n    Weighted n
    #> ───────────────────────────────┼─────────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │    66.52      <.001  0.19  1200   1196.47
    #>  Body mass index               │    26.16      <.001  0.13  1188   1183.32

This is often the most natural summary-table function when your reporting workflow already relies on weighted linear models.

## Numeric predictors

If `by` is numeric, `table_continuous_lm()` reports the slope rather than group means:

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = age,
      vcov = "HC3"
    )
    #> Continuous outcomes by Age (years)
    #>
    #>  Variable                      │  B    95% CI LL  95% CI UL    p     R²    n
    #> ───────────────────────────────┼───────────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │ 0.04    -0.02      0.10      .176  0.00  1200
    #>  Body mass index               │ 0.04     0.02      0.05     <.001  0.02  1188

When you need the underlying returned data for further processing, use `output = "data.frame"` for the wide raw table or `output = "long"` for the analytic long table.

## Effect sizes

`table_continuous_lm()` supports four effect sizes via the `effect_size` argument. All are derived from the same fitted model as the displayed coefficients and `R²`, so the table stays internally consistent — and all are invariant to `vcov` (the choice of classical or `HC*` standard errors changes the contrast SE, CI, and test statistic but not the standardized effect size itself).

Cohen’s d and Hedges’ g are the conventions for two-group comparisons (Cohen 1988; Hedges and Olkin 1985; APA 2020) and require `by` to have exactly two non-empty levels:

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = smoking,
      effect_size = "d"
    )
    #> Continuous outcomes by Current smoker
    #>
    #>  Variable                      │ M (No)  M (Yes)  Δ (Yes - No)  95% CI LL
    #> ───────────────────────────────┼──────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │ 69.36    67.65      -1.72        -3.91
    #>  Body mass index               │ 25.96    25.93      -0.03        -0.55
    #>
    #>  Variable                      │ 95% CI UL   p     R²     d     n
    #> ───────────────────────────────┼────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │   0.47     .124  0.00  -0.11  1175
    #>  Body mass index               │   0.49     .905  0.00  -0.01  1163

Hedges’ g applies the small-sample correction `J = 1 - 3/(4·df_resid - 1)`. It is generally preferred over raw d in published reports (Goulet-Pelletier and Cousineau 2018):

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = smoking,
      effect_size = "g"
    )
    #> Continuous outcomes by Current smoker
    #>
    #>  Variable                      │ M (No)  M (Yes)  Δ (Yes - No)  95% CI LL
    #> ───────────────────────────────┼──────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │ 69.36    67.65      -1.72        -3.91
    #>  Body mass index               │ 25.96    25.93      -0.03        -0.55
    #>
    #>  Variable                      │ 95% CI UL   p     R²     g     n
    #> ───────────────────────────────┼────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │   0.47     .124  0.00  -0.11  1175
    #>  Body mass index               │   0.49     .905  0.00  -0.01  1163

For categorical predictors with three or more levels (or numeric predictors), use Hays’ `omega²` for a less biased estimate of the population variance explained (Hays 1963; Olejnik and Algina 2003; Lakens 2013):

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = education,
      effect_size = "omega2"
    )
    #> Continuous outcomes by Highest education level
    #>
    #>  Variable                      │ M (Lower secondary)  M (Upper secondary)
    #> ───────────────────────────────┼──────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │        67.68                81.56
    #>  Body mass index               │        26.17                23.55
    #>
    #>  Variable                      │ M (Tertiary)    p     R²    ω²    n
    #> ───────────────────────────────┼───────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │    66.10      <.001  0.21  0.21  1200
    #>  Body mass index               │    26.35      <.001  0.13  0.13  1188

Cohen’s `f²` (= `R² / (1 - R²)`) is the effect size familiar from power-analysis frameworks (e.g. G*Power) and is defined for any predictor type:

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = age,
      effect_size = "f2"
    )
    #> Continuous outcomes by Age (years)
    #>
    #>  Variable                      │  B    95% CI LL  95% CI UL    p     R²    f²
    #> ───────────────────────────────┼───────────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │ 0.04    -0.02      0.10      .177  0.00  0.00
    #>  Body mass index               │ 0.04     0.02      0.05     <.001  0.02  0.02
    #>
    #>  Variable                      │  n
    #> ───────────────────────────────┼──────
    #>  WHO-5 wellbeing index (0-100) │ 1200
    #>  Body mass index               │ 1188

## Confidence intervals for effect sizes

Setting `effect_size_ci = TRUE` adds a confidence interval for the effect size. The implementation uses the modern noncentral-distribution inversion approach — the consensus standard in commercial statistical software (Stata `esize` / `estat esize`, SAS `PROC TTEST` and `PROC GLM EFFECTSIZE`) and in mainstream R packages (`effectsize`, `MOTE`, `TOSTER`, `effsize`):

- Noncentral t inversion for `"d"` and `"g"` (Steiger and Fouladi 1997; Goulet-Pelletier and Cousineau 2018; Cousineau and Goulet-Pelletier 2021), which has nominal coverage across sample sizes — unlike the older Hedges-Olkin normal approximation that is biased for small samples.
- Noncentral F inversion for `"omega2"` and `"f2"` (Steiger 2004; Smithson 2003).

In the printed and rendered outputs, the effect size is displayed with the bracketed CI (article-ready):

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = smoking,
      effect_size = "g",
      effect_size_ci = TRUE
    )
    #> Continuous outcomes by Current smoker
    #>
    #>  Variable                      │ M (No)  M (Yes)  Δ (Yes - No)  95% CI LL
    #> ───────────────────────────────┼──────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │ 69.36    67.65      -1.72        -3.91
    #>  Body mass index               │ 25.96    25.93      -0.03        -0.55
    #>
    #>  Variable                      │ 95% CI UL   p     R²            g
    #> ───────────────────────────────┼────────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │   0.47     .124  0.00  -0.11 [-0.25, 0.03]
    #>  Body mass index               │   0.49     .905  0.00  -0.01 [-0.15, 0.13]
    #>
    #>  Variable                      │  n
    #> ───────────────────────────────┼──────
    #>  WHO-5 wellbeing index (0-100) │ 1175
    #>  Body mass index               │ 1163

The CI level follows `ci_level` (default `0.95`). For programmatic access, the wide raw output exposes separate numeric columns, and the long output always includes them:

    table_continuous_lm(
      sochealth,
      select = wellbeing_score,
      by = smoking,
      effect_size = "g",
      effect_size_ci = TRUE,
      output = "data.frame"
    )
    #>                                      Variable   M (No)  M (Yes) Δ (Yes - No)
    #> wellbeing_score WHO-5 wellbeing index (0-100) 69.36317 67.64538    -1.717793
    #>                 95% CI LL 95% CI UL         p          R²          g
    #> wellbeing_score -3.906437 0.4708504 0.1238546 0.002017481 -0.1098571
    #>                 effect_size_ci_lower effect_size_ci_upper    n
    #> wellbeing_score           -0.2497291           0.03006164 1175

    out <- table_continuous_lm(
      sochealth,
      select = wellbeing_score,
      by = smoking,
      effect_size = "g",
      effect_size_ci = TRUE,
      output = "long"
    )
    out[, c("variable", "es_type", "es_value", "es_ci_lower", "es_ci_upper")]
    #>          variable es_type   es_value es_ci_lower es_ci_upper
    #> 1 wellbeing_score       g -0.1098571  -0.2497291  0.03006164
    #> 2 wellbeing_score    <NA>         NA          NA          NA

When `weights` is supplied, all four effect sizes (and their CIs) are computed from the weighted least-squares fit, keeping them consistent with the weighted contrast and its CI (DuMouchel and Duncan 1983). This is the right convention for case-weighted reporting; for propensity-score balance assessment (Austin and Stuart 2015) or complex-survey designs, dedicated packages (`cobalt::bal.tab()` and `survey`) are more appropriate.

## Article-style polish

Pretty outcome labels and a comma decimal separator (useful for European reporting):

    table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = sex,
      labels = c(
        wellbeing_score = "WHO-5 wellbeing (0-100)",
        bmi = "Body-mass index (kg/m²)"
      ),
      effect_size = "g",
      effect_size_ci = TRUE,
      decimal_mark = ","
    )
    #> Continuous outcomes by Sex
    #>
    #>  Variable                │ M (Female)  M (Male)  Δ (Male - Female)  95% CI LL
    #> ─────────────────────────┼────────────────────────────────────────────────────
    #>  WHO-5 wellbeing (0-100) │   67,16      71,05          3,89           2,13
    #>  Body-mass index (kg/m²) │   25,69      26,20          0,51           0,09
    #>
    #>  Variable                │ 95% CI UL    p     R²           g           n
    #> ─────────────────────────┼─────────────────────────────────────────────────
    #>  WHO-5 wellbeing (0-100) │   5,64     <,001  0,02  0,25 [0,14; 0,36]  1200
    #>  Body-mass index (kg/m²) │   0,93      ,018  0,00  0,14 [0,02; 0,25]  1188

## Publication-ready output

The function supports the same output formats as the other summary-table helpers, including `tinytable`, `gt`, `flextable`, `excel`, `word`, and `clipboard`.

    pkgdown_dark_gt(
      table_continuous_lm(
        sochealth,
        select = c(wellbeing_score, bmi, life_sat_health),
        by = sex,
        vcov = "HC3",
        statistic = TRUE,
        output = "gt"
      )
    )

## Tidying for downstream pipelines

`table_continuous_lm()` returns an object that can be coerced to a plain `data.frame` / `tbl_df` (stripping the spicy formatting attributes) or piped into `broom::tidy()` / `broom::glance()` for use with `gtsummary`, `modelsummary`, `parameters`, or any other tidyverse-stats workflow:

    out <- table_continuous_lm(
      sochealth,
      select = c(wellbeing_score, bmi),
      by = sex,
      effect_size = "g",
      effect_size_ci = TRUE
    )
    #> Continuous outcomes by Sex
    #>
    #>  Variable                      │ M (Female)  M (Male)  Δ (Male - Female)
    #> ───────────────────────────────┼─────────────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │   67.16      71.05          3.89
    #>  Body mass index               │   25.69      26.20          0.51
    #>
    #>  Variable                      │ 95% CI LL  95% CI UL    p     R²
    #> ───────────────────────────────┼───────────────────────────────────
    #>  WHO-5 wellbeing index (0-100) │   2.13       5.64     <.001  0.02
    #>  Body mass index               │   0.09       0.93      .018  0.00
    #>
    #>  Variable                      │         g           n
    #> ───────────────────────────────┼─────────────────────────
    #>  WHO-5 wellbeing index (0-100) │ 0.25 [0.14, 0.36]  1200
    #>  Body mass index               │ 0.14 [0.02, 0.25]  1188

    # One row per estimated parameter: emmean per level, contrast for
    # binary predictors, slope for numeric predictors.
    broom::tidy(out)
    #> # A tibble: 6 × 10
    #>   outcome        label term  estimate_type estimate std.error conf.low conf.high
    #>   <chr>          <chr> <chr> <chr>            <dbl>     <dbl>    <dbl>     <dbl>
    #> 1 wellbeing_sco… WHO-… Fema… emmean          67.2       0.623  65.9       68.4
    #> 2 wellbeing_sco… WHO-… Male  emmean          71.0       0.644  69.8       72.3
    #> 3 wellbeing_sco… WHO-… Male… difference       3.89      0.896   2.13       5.64
    #> 4 bmi            Body… Fema… emmean          25.7       0.150  25.4       26.0
    #> 5 bmi            Body… Male  emmean          26.2       0.155  25.9       26.5
    #> 6 bmi            Body… Male… difference       0.512     0.216   0.0888     0.935
    #> # ℹ 2 more variables: statistic <dbl>, p.value <dbl>

    # One row per outcome with model-level statistics: r.squared,
    # adj.r.squared, F / t, df, p.value, nobs, weighted_n, plus the
    # effect-size summary.
    broom::glance(out)
    #> # A tibble: 2 × 16
    #>   outcome     label predictor_type test_type statistic    df df.residual p.value
    #>   <chr>       <chr> <chr>          <chr>         <dbl> <int>       <int>   <dbl>
    #> 1 wellbeing_… WHO-… categorical    F             18.8      1        1198 1.55e-5
    #> 2 bmi         Body… categorical    F              5.64     1        1186 1.78e-2
    #> # ℹ 8 more variables: r.squared <dbl>, adj.r.squared <dbl>, es_type <chr>,
    #> #   es_value <dbl>, es_ci_lower <dbl>, es_ci_upper <dbl>, nobs <int>,
    #> #   weighted_n <dbl>

## See also

- See `vignette("table-continuous", package = "spicy")` for descriptive continuous summary tables with classical group-comparison tests.
- See `vignette("summary-tables-reporting", package = "spicy")` for a cross-function reporting workflow using the summary-table helpers.