Forest plots provide a graphical representation of effect estimates and their precision. Each row displays a point estimate (typically an odds ratio, hazard ratio, or regression coefficient) with a confidence interval, enabling rapid visual assessment of effect magnitude, direction, and statistical significance. The format is standard in published research and regulatory submissions.

The summata package provides specialized forest plot functions for each model type, plus an automatic detection function:

Function	Model Type	Effect Measure
`autoforest()`	Auto-detect	Auto-detect
`lmforest()`	Linear regression	Coefficient (β)
`glmforest()`	Logistic/Poisson	Odds ratio / Rate ratio
`coxforest()`	Cox regression	Hazard ratio
`uniforest()`	Univariable screening	Model-dependent
`multiforest()`	Multi-outcome analysis	Model-dependent

where x is either a model or a summata fitted output (e.g., from uniscreen(), fit(), fullfit(), or multifit()), and data is the name of the dataset used. The data argument is optional and is primarily used to derive n and Events counts for various groups/subgroups.

All forest plot functions produce ggplot2 objects that can be further customized. As such, they can also be exported to various external formats such as PDF, PNG, TIFF, JPEG, SVG, EPS, and other file types supported by ggplot2::ggsave(). This export can be streamlined with summata-recommended default dimensions by using the forestsave() function:

This vignette demonstrates the various capabilities of these functions using the included sample dataset.

Preliminaries

The examples in this vignette use the clintrial dataset included with summata:

library(summata)
library(survival)
library(ggplot2)

data(clintrial)
data(clintrial_labels)

n.b.: The forest plots below are sized by this vignette from each plot’s recommended dimensions, stored in its "rec_dims" attribute, and rendered via the ragg graphics device for correct font metrics. That sizing is applied behind the scenes and is not shown in the code. Writing a plot to file elsewhere is performed with forestsave(), which applies the same dimensions and selects a suitable graphics device:
p <- glmforest(model, data = mydata)
forestsave(p, "forest_plot.png")
This ensures that the figure size is always large enough to accommodate the constituent plot text and graphics, and it is the preferred method for saving forest plot outputs in summata.

Creating Forest Plots from Model Objects

Forest plots can be created from standard R model objects or from summata function output.

Example 1: Logistic Regression

Fit a model using base R, then create a forest plot:

logistic_model <- glm(
  surgery ~ age + sex + stage + treatment + ecog,
  data = clintrial,
  family = binomial
)

example1 <- glmforest(
  x = logistic_model,
  data = clintrial,
  title = "Logistic Regression: Predictors of Outcome",
  labels = clintrial_labels
)

Example 2: Linear Regression

For continuous outcomes, use lmforest():

linear_model <- lm(
  los_days ~ age + sex + stage + surgery + ecog,
  data = clintrial
)

example2 <- lmforest(
  x = linear_model,
  data = clintrial,
  title = "Linear Regression: Length of Stay",
  labels = clintrial_labels
)

Example 3: Cox Regression

For survival models, use coxforest():

cox_model <- coxph(
  Surv(os_months, os_status) ~ age + sex + stage + treatment + ecog,
  data = clintrial
)

example3 <- coxforest(
  x = cox_model,
  data = clintrial,
  title = "Cox Regression: Survival Analysis",
  labels = clintrial_labels
)

Example 4: Automatic Model Detection

The autoforest() function detects the model type automatically:

example4 <- autoforest(
  x = cox_model,
  data = clintrial,
  labels = clintrial_labels
)

Creating Forest Plots from summata Output

Forest plots integrate seamlessly with fit() and fullfit() output by extracting the attached model object.

Example 5: Direct Extraction from Fit Output

Input a summata regression object (i.e., from fit() or fullfit()) directly into a forest plot function:

table_logistic <- fit(
  data = clintrial,
  outcome = "surgery",
  predictors = c("age", "sex", "stage", "treatment", "ecog"),
  model_type = "glm",
  labels = clintrial_labels
)

example5 <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Predictors of Surgical Intervention",
  labels = clintrial_labels,
  zebra_stripes = TRUE
)

Example 6: Model Attribute from Fit Output

Alternatively, input the attached model attribute from a summata regression object:

table_cox <- fit(
  data = clintrial,
  outcome = "Surv(os_months, os_status)",
  predictors = c("age", "sex", "stage", "treatment", "ecog"),
  model_type = "coxph",
  labels = clintrial_labels
)

example6 <- coxforest(
  x = attr(table_cox, "model"),
  title = "Predictors of Overall Survival",
  labels = clintrial_labels,
  zebra_stripes = TRUE
)

Display Options

Example 7: Indenting Factor Levels

The indent_groups parameter creates hierarchical display for a more compact aesthetic:

example7 <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Indented Factor Levels",
  labels = clintrial_labels,
  indent_groups = TRUE
)

Example 8: Condensing Binary Variables

The condense_table parameter displays binary variables on single rows. Group indenting is applied automatically:

example8 <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Condensed Display",
  labels = clintrial_labels,
  condense_table = TRUE
)

Example 9: Toggle Zebra Striping

Zebra striping is enabled by default. It can be disabled via zebra_stripes = FALSE:

example9 <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Without Zebra Striping",
  labels = clintrial_labels,
  indent_groups = TRUE,
  zebra_stripes = FALSE
)

Example 10: Sample Size and Event Columns

Control display of sample size (n) and event counts:

# Show both n and events
example10a <- coxforest(
  x = attr(table_cox, "model"),
  title = "With Sample Size and Events",
  labels = clintrial_labels,
  show_n = TRUE,
  show_events = TRUE,
  indent_groups = TRUE,
  zebra_stripes = TRUE
)

# Minimal display
example10b <- coxforest(
  x = attr(table_cox, "model"),
  title = "Minimal Display",
  labels = clintrial_labels,
  show_n = FALSE,
  show_events = FALSE,
  indent_groups = TRUE
)

Formatting Options

Example 11: Adjusting Numeric Precision

The digits parameter controls decimal places for effect estimates and confidence intervals:

example11 <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Custom Precision (3 decimal places)",
  labels = clintrial_labels,
  digits = 3,
  indent_groups = TRUE
)

Example 12: Custom Reference Label

Customize the label shown for reference categories:

example12 <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Custom Reference Label",
  labels = clintrial_labels,
  ref_label = "ref",
  indent_groups = TRUE
)

Example 13: Custom Effect Measure Label

Change the column header for the effect measure:

example13 <- coxforest(
  x = attr(table_cox, "model"),
  title = "Custom Effect Label",
  labels = clintrial_labels,
  effect_label = "Effect (95% CI)",
  indent_groups = TRUE
)

Example 14: Custom Colors

The color parameter changes the point and line color:

example14 <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Custom Color",
  labels = clintrial_labels,
  color = "#E41A1C",
  indent_groups = TRUE
)

Example 15: Change Font Sizes

Adjust text size with the font_size multiplier:

example15 <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Larger Font (1.5×)",
  labels = clintrial_labels,
  font_size = 1.5,
  indent_groups = TRUE,
  qc_footer = FALSE
)

Example 16: Table Width

The table_width parameter adjusts the proportion of space allocated to the table vs. the forest plot:

# Wide table (for long variable names)
example16a <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Wide Table (75%)",
  labels = clintrial_labels,
  table_width = 0.75
)

# Narrow table (emphasizes forest plot)
example16b <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Narrow Table (50%)",
  labels = clintrial_labels,
  table_width = 0.50
)

Saving Forest Plots

Forest plots include a rec_dims attribute recording the dimensions best suited to their content. forestsave() reads it, so no manual sizing is required.

Example 17: Recommended Dimensions

recdims() can be used to extract the recommended plot dimensions directly.

p <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Publication-Ready Plot",
  labels = clintrial_labels,
  indent_groups = TRUE,
  zebra_stripes = TRUE
)

# The recommended dimensions, in the units in which the plot was created
recdims(p)
##>  width height 
##>   13.4    7.5 
##> attr(,"units")
##> [1] "in"

# Journals commonly specify figure widths in millimeters
recdims(p, units = "mm")
##>  width height 
##> 340.36 190.50 
##> attr(,"units")
##> [1] "mm"

Example 18: Multiple Formats

Export to different formats as needed using forestsave():

p <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Forest Plot",
  labels = clintrial_labels
)

# The format follows the file extension, and the dimensions are applied
# automatically in every case

# PDF (vector, best for publications)
forestsave(p, "forest.pdf")

# PNG (raster, good for presentations)
forestsave(p, "forest.png", dpi = 300)

# TIFF (high-quality raster, often required by journals)
forestsave(p, "forest.tiff", dpi = 300)

# SVG (vector, good for web)
forestsave(p, "forest.svg")

Advanced Customization

Forest plots support extensive customization for publication requirements.

Example 19: Combined Options

Combine multiple options for publication-ready output:

example19 <- coxforest(
  x = attr(table_cox, "model"),
  title = "Comprehensive Survival Analysis",
  labels = clintrial_labels,
  effect_label = "Hazard Ratio",
  digits = 2,
  show_n = TRUE,
  show_events = TRUE,
  indent_groups = TRUE,
  condense_table = FALSE,
  zebra_stripes = TRUE,
  ref_label = "reference",
  font_size = 1.0,
  table_width = 0.62,
  color = "#B5394C"
)

Example 20: Extensions with ggplot2

Forest plots are ggplot2 objects and can be modified further:

example20 <- glmforest(
  x = attr(table_logistic, "model"),
  title = "Extended with ggplot2",
  labels = clintrial_labels,
  indent_groups = TRUE
)

example20_modified <- example20 +
  theme(
    plot.title = element_text(face = "italic", color = "#A72727"),
    plot.background = element_rect(fill = "white", color = NA)
  )

Additional GLM Families

The glmforest() function supports all GLM families. These can be plotted in a similar fashion to standard logistic regression forest plots. See Regression Modeling for the full list of supported model types.

Example 21: Poisson Regression

For equidispersed count outcomes (variance ≈ mean), use Poisson regression:

poisson_model <- glm(
  fu_count ~ age + stage + treatment + surgery,
  data = clintrial,
  family = poisson
)

example21 <- glmforest(
  x = poisson_model,
  data = clintrial,
  title = "Poisson Regression: Follow-Up Visits",
  labels = clintrial_labels
)

Example 22: Negative Binomial Regression

For overdispersed count outcomes (variance > mean), negative binomial regression is preferred. Using fit() ensures proper handling:

nb_result <- fit(
  data = clintrial,
  outcome = "ae_count",
  predictors = c("age", "treatment", "diabetes", "surgery"),
  model_type = "negbin",
  labels = clintrial_labels
)

example22 <- glmforest(
  x = nb_result,
  title = "Negative Binomial: Adverse Events"
)

Function Parameter Summary

Parameter	Description	Default
`x`	Model object or model from `fit()` output	Required
`data`	Data frame (required for model objects)	`NULL`
`title`	Plot title	`NULL`
`labels`	Named vector for variable labels	`NULL`
`indent_groups`	Indent factor levels under variable names	`FALSE`
`condense_table`	Show binary variables on single row	`FALSE`
`zebra_stripes`	Alternating row shading	`TRUE`
`show_n`	Display sample size column	`TRUE`
`show_events`	Display events column (Cox models)	`TRUE`
`digits`	Decimal places for estimates	`2`
`ref_label`	Label for reference categories	`"reference"`
`effect_label`	Column header for effect measure	Model-dependent
`color`	Color for points and lines	Effect-type dependent
`font_size`	Text size multiplier	`1.0`
`table_width`	Proportion of width for table	`0.55`

Best Practices

Model Preparation

Ensure all factor levels are properly defined before fitting
Use meaningful reference categories
Consider centering continuous variables for interpretability
Check model convergence before plotting

Visual Design

Use indent_groups = TRUE for cleaner presentation of categorical variables
Match table_width to variable name lengths
Consider condense_table = TRUE for binary predictors
Use consistent colors across related figures

Publication Preparation

Use rec_dims attribute for optimal sizing
Save as PDF for vector graphics in print
Use 300+ DPI for raster formats
Check that reference lines and confidence intervals are clearly visible

Common Issues

Long Variable Names

If variable names are truncated, increase table_width:

p <- glmforest(model, table_width = 0.75)

Overlapping Text

Reduce font size or increase figure dimensions:

p <- glmforest(model, font_size = 0.9)
forestsave(p, "plot.pdf", width = 14, height = 8)

Missing Labels

Ensure labels vector includes all variable names:

labels <- c(
  age = "Age (years)",
  sex = "Sex",
  stage = "Disease Stage"
)
p <- glmforest(model, labels = labels)

Forest Plots