Regression Methods: Multiple and Logistic RWA"

In rwa: Perform a Relative Weights Analysis

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>",
  out.width = "100%",
  error = FALSE,
  warning = FALSE,
  message = FALSE
)

library(rwa)
library(dplyr)
library(ggplot2)

Introduction

The rwa package provides two specialized functions for conducting Relative Weights Analysis depending on the nature of your outcome variable:

• rwa_multiregress(): For continuous outcome variables (standard multiple regression)
• rwa_logit(): For binary outcome variables (logistic regression)

The main rwa() function acts as a convenient wrapper that can automatically detect which method to use, but understanding these underlying functions gives you more control and insight into your analysis.

When to Use Each Method

| Outcome Type | Function | Example Use Cases | |--------------|----------|-------------------| | Continuous | rwa_multiregress() | Predicting prices, scores, measurements | | Binary (0/1) | rwa_logit() | Predicting yes/no, pass/fail, purchase/no purchase |

Multiple Regression with rwa_multiregress()

Basic Example with mtcars

The mtcars dataset contains continuous variables ideal for demonstrating multiple regression RWA. Let's examine what factors most influence fuel efficiency (mpg):

# Direct use of rwa_multiregress()
result_multi <- rwa_multiregress(
  df = mtcars,
  outcome = "mpg",
  predictors = c("cyl", "disp", "hp", "wt")
)

# View results
result_multi$result

Interpreting Multiple Regression Results

The output contains several key pieces of information:

# R-squared: Total variance explained
cat("R-squared:", round(result_multi$rsquare, 4), "\n")
cat("This means", round(result_multi$rsquare * 100, 1), 
    "% of variance in mpg is explained by these predictors.\n\n")

# Number of observations
cat("Sample size:", result_multi$n, "\n\n")

# Relative importance breakdown
cat("Relative Importance (Rescaled Weights sum to 100%):\n")
result_multi$result %>%
  arrange(desc(Rescaled.RelWeight)) %>%
  mutate(Rescaled.RelWeight = round(Rescaled.RelWeight, 2)) %>%
  select(Variables, Rescaled.RelWeight)

The Rescaled.RelWeight column shows the percentage of explainable variance attributed to each predictor. In this example, we can see that weight (wt) is the most important predictor of fuel efficiency, followed by displacement (disp).

Using the applysigns Parameter

By default, relative weights are always positive (they represent variance contributions). Use applysigns = TRUE to see the direction of each relationship:

# With sign information
result_signed <- rwa_multiregress(
  df = mtcars,
  outcome = "mpg",
  predictors = c("cyl", "disp", "hp", "wt"),
  applysigns = TRUE
)

result_signed$result %>%
  select(Variables, Raw.RelWeight, Sign.Rescaled.RelWeight, Sign)

The Sign column indicates whether each predictor has a positive (+) or negative (-) relationship with the outcome. Negative signs for cyl, disp, hp, and wt make intuitive sense: more cylinders, larger displacement, more horsepower, and heavier weight all tend to decrease fuel efficiency.

Examining Correlation Structures

The function also returns the correlation matrices, which can help understand relationships between predictors:

# Correlation between predictors
cat("Predictor Correlation Matrix (RXX):\n")
round(result_multi$RXX, 3)

# Correlation of predictors with outcome
cat("\nPredictor-Outcome Correlations (RXY):\n")
round(result_multi$RXY, 3)

Logistic Regression with rwa_logit()

Creating a Binary Outcome

For logistic regression, we need a binary outcome variable. Let's create one from the mtcars dataset:

# Create binary outcome: high efficiency (1) vs low efficiency (0)
mtcars_binary <- mtcars %>%
  mutate(high_mpg = ifelse(mpg > median(mpg), 1, 0))

# Check distribution
table(mtcars_binary$high_mpg)

Basic Logistic RWA

# Logistic regression RWA
result_logit <- rwa_logit(
  df = mtcars_binary,
  outcome = "high_mpg",
  predictors = c("cyl", "disp", "hp", "wt")
)

# View results
result_logit$result

Interpreting Logistic RWA Results

The interpretation differs slightly from multiple regression:

# Lambda (analogous to R-squared for logistic regression)
cat("Lambda (pseudo R-squared):", round(result_logit$lambda, 4), "\n")
cat("Sample size:", result_logit$n, "\n\n")

# Relative importance
cat("Relative Importance for Predicting High Fuel Efficiency:\n")
result_logit$result %>%
  arrange(desc(Rescaled.RelWeight)) %>%
  mutate(Rescaled.RelWeight = round(Rescaled.RelWeight, 2))

Like multiple regression, the Rescaled.RelWeight values sum to 100%, representing the percentage of predictable variance attributed to each predictor.

Logistic RWA with Signs

# With direction information
result_logit_signed <- rwa_logit(
  df = mtcars_binary,
  outcome = "high_mpg",
  predictors = c("cyl", "disp", "hp", "wt"),
  applysigns = TRUE
)

result_logit_signed$result %>%
  select(Variables, Rescaled.RelWeight, Sign)

Using the rwa() Wrapper Function

The main rwa() function provides a convenient interface that can automatically detect whether to use multiple or logistic regression based on your outcome variable.

Auto-Detection of Binary Outcomes

# For continuous outcome - automatically uses multiple regression
result_auto_multi <- rwa(
  df = mtcars,
  outcome = "mpg",
  predictors = c("cyl", "disp", "hp", "wt")
)

# For binary outcome - automatically uses logistic regression
result_auto_logit <- rwa(
  df = mtcars_binary,
  outcome = "high_mpg",
  predictors = c("cyl", "disp", "hp", "wt")
)

Explicit Method Selection

You can also explicitly specify the method using the method parameter:

# Force multiple regression
result_explicit_multi <- rwa(
  df = mtcars,
  outcome = "mpg",
  predictors = c("cyl", "disp", "hp", "wt"),
  method = "multiple"
)

# Force logistic regression (requires binary outcome)
result_explicit_logit <- rwa(
  df = mtcars_binary,
  outcome = "high_mpg",
  predictors = c("cyl", "disp", "hp", "wt"),
  method = "logistic"
)

Additional Features in rwa()

The wrapper function also provides sorting and visualization options:

# Sort results by importance
result_sorted <- rwa(
  df = mtcars,
  outcome = "mpg",
  predictors = c("cyl", "disp", "hp", "wt"),
  sort = TRUE
)

result_sorted$result

# Visualize with plot_rwa()
plot_rwa(result_sorted)

The use and weight arguments apply to multiple regression only. Neither affects a logistic fit. rwa() warns when you supply a weight column or a non-default use value alongside logistic RWA, and ignores them, because rwa_logit() does not fit a weighted or correlation-based model:

# Weighted RWA: multiple regression only
rwa(df, "satisfaction", c("x1", "x2"), weight = "survey_weight")

# Warns, and the weight is not applied
rwa(df, "binary_outcome", c("x1", "x2"), weight = "survey_weight")

See vignette("weighted-missing-data", package = "rwa") for weighted estimation and the missing-data contract.

Real-World Example: Iris Dataset

Let's apply these methods to the classic iris dataset.

Multiple Regression: Predicting Petal Length

# Predict petal length from other measurements
iris_result <- rwa_multiregress(
  df = iris,
  outcome = "Petal.Length",
  predictors = c("Sepal.Length", "Sepal.Width", "Petal.Width"),
  applysigns = TRUE
)

cat("R-squared:", round(iris_result$rsquare, 4), "\n\n")
iris_result$result

# Visualize
plot_rwa(iris_result)

Logistic Regression: Predicting Species

For logistic regression, we need a binary outcome. Let's predict whether a flower is Iris setosa or not:

# Create binary outcome for setosa classification
iris_binary <- iris %>%
  mutate(is_setosa = ifelse(Species == "setosa", 1, 0))

# Logistic RWA
iris_logit <- rwa_logit(
  df = iris_binary,
  outcome = "is_setosa",
  predictors = c("Sepal.Length", "Sepal.Width", "Petal.Length", "Petal.Width"),
  applysigns = TRUE
)

cat("Pseudo R-squared:", round(iris_logit$rsquare, 4), "\n\n")
iris_logit$result

This analysis reveals which measurements are most important for distinguishing Iris setosa from the other species.

Comparing Methods

Let's demonstrate how the same predictors can yield different importance rankings depending on the outcome type:

# Create comparison dataset
comparison_data <- mtcars %>%
  mutate(high_mpg = ifelse(mpg > median(mpg), 1, 0))

# Multiple regression on continuous mpg
multi_result <- rwa_multiregress(
  comparison_data, "mpg", 
  c("cyl", "disp", "hp", "wt")
)

# Logistic regression on binary high_mpg
logit_result <- rwa_logit(
  comparison_data, "high_mpg", 
  c("cyl", "disp", "hp", "wt")
)

# Compare rankings
comparison <- data.frame(
  Variable = multi_result$result$Variables,
  Multiple_Pct = round(multi_result$result$Rescaled.RelWeight, 1),
  Logistic_Pct = round(logit_result$result$Rescaled.RelWeight, 1)
)

comparison %>%
  arrange(desc(Multiple_Pct))

The relative importance of predictors may differ between continuous and binary outcomes because:

1. Different relationships: A predictor's linear relationship with the continuous outcome may differ from its relationship with the probability of the binary outcome.
2. Threshold effects: Binary outcomes are sensitive to whether predictors help distinguish cases near the classification boundary.

Best Practices

1. Choose the Right Method

• Use rwa_multiregress() for continuous outcomes
• Use rwa_logit() for binary (0/1) outcomes
• Let rwa() auto-detect when unsure

2. Check Your Data

# Always check outcome distribution for binary variables
table(mtcars_binary$high_mpg)

# Ensure reasonable sample size
cat("Sample size:", nrow(mtcars), "\n")
cat("Predictors:", 4, "\n")
cat("Observations per predictor:", nrow(mtcars) / 4, "\n")

A general guideline is to have at least 10-20 observations per predictor.

3. Consider Bootstrap for Inference

For statistical significance testing, combine with bootstrap methods (note: currently only available for multiple regression):

# Bootstrap with multiple regression
result_boot <- rwa(
  df = mtcars,
  outcome = "mpg",
  predictors = c("cyl", "disp", "hp", "wt"),
  bootstrap = TRUE,
  n_bootstrap = 1000
)

result_boot$result

Summary

| Function | Outcome Type | Key Output | Weights Sum To | |----------|--------------|------------|----------------| | rwa_multiregress() | Continuous | R², Raw & Rescaled Weights | 100% | | rwa_logit() | Binary (0/1) | R², Raw & Rescaled Weights | 100% | | rwa() | Either | Auto-detects + sorting + bootstrap | 100% |

Both methods provide valuable insights into predictor importance while accounting for multicollinearity. Choose the appropriate method based on your outcome variable type, and consider using bootstrap confidence intervals for formal statistical inference.

References

• Johnson, J. W. (2000). A heuristic method for estimating the relative weight of predictor variables in multiple regression. Multivariate Behavioral Research, 35(1), 1-19.

• Tonidandel, S., & LeBreton, J. M. (2011). Relative importance analysis: A useful supplement to regression analysis. Journal of Business and Psychology, 26(1), 1-9.

• Tonidandel, S., & LeBreton, J. M. (2015). RWA Web: A free, comprehensive, web-based, and user-friendly tool for relative weight analyses. Journal of Business and Psychology, 30(2), 207-216.

rwa documentation built on Sept. 29, 2026, 1:06 a.m.