Statistical Significance Annotation on Plots

Statistical Significance Annotation on Plots

Overview

Statistical significance annotations (asterisk notation) are visual markers placed on comparison plots to indicate the results of hypothesis tests between groups. They consist of brackets connecting two groups and asterisk symbols denoting the p-value range. Proper annotation ensures that the visual claims in a figure match the quantitative evidence, making plots publication-ready and scientifically rigorous. This guide covers the standard conventions, when and how to annotate, and a reusable matplotlib implementation.

Key Concepts

Standard Asterisk Notation

The widely adopted convention maps p-value ranges to asterisk symbols:

The conversion function:

def pvalue_to_asterisk(p: float) -> str:
    """Convert a p-value to standard asterisk notation."""
    if p <= 0.0001:
        return "****"
    elif p <= 0.001:
        return "***"
    elif p <= 0.01:
        return "**"
    elif p <= 0.05:
        return "*"
    else:
        return "ns"

Adjusted vs Raw P-values

• Single comparison (one t-test): Use raw p-value.