HolobiomicsLab 
FDR correction for multiple testing
Summary
Apply Benjamini–Hochberg false discovery rate correction to empirical p-values derived from randomized sampling to control Type I error across reaction-level regulatory classifications. This ensures that significance thresholds account for the multiple hypothesis tests performed on thousands of metabolic reactions.
When to use
You have computed empirical p-values from randomized sampling (e.g., via resampling of RPS scores or Mann–Whitney U tests across multiple reaction-level comparisons) and need to set a single, multiple-testing-corrected significance threshold that applies uniformly across all reactions in a metabolic network. Use this when the number of reactions tested is large (>100) and you want to control genome-scale false discovery rather than per-reaction type I error.
When NOT to use
- Input is a small number of reactions (< 20 total tested) where Benjamini–Hochberg correction may be overly conservative and Bonferroni or no correction is more appropriate.
- P-values are not empirically derived or do not have a clear null distribution (e.g., analytical p-values without resampling support).
- You are testing a single reaction in isolation or performing post-hoc hypothesis testing on a pre-selected subset of reactions, where FDR correction designed for genome-scale testing is inappropriate.
Inputs
- empirical p-values (one per metabolic reaction, derived from randomized sampling or Mann–Whitney U tests)
- reaction identifiers (SBML reaction IDs, e.g. 'ACONT', 'PFK')
- Cohen's kappa concordance coefficients (RASvsFFD, RPSvsFFD, RPSvsRAS)
Outputs
- FDR-adjusted p-values (one per reaction)
- significance assignment (binary: pass/fail at FDR < 0.05)
- filtered reaction classification table (only reactions meeting FDR threshold)
- summary statistics (number and fraction of reactions retained after correction)
How to apply
After computing empirical p-values for each reaction (e.g., from randomized RPS sampling or Mann–Whitney U tests on flux distributions), apply the Benjamini–Hochberg procedure: rank p-values in ascending order, compute adjusted p-values using the formula p_adj = p × (m / rank), where m is the total number of reactions tested, then filter to retain only reactions with FDR-adjusted p-value < 0.05 (or your chosen alpha). This correction is applied before classifying reactions into regulatory categories (combined, metabolic-only, transcriptional-only, or unclassified) to ensure that only statistically robust concordance signatures are assigned a regulatory class. Document the number of reactions passing the FDR threshold and compare to unadjusted counts to assess the stringency of the correction.
Related tools
- COBRApy (constraint-based sampling and reaction enumeration for multi-hypothesis testing context) — https://github.com/opencobra/cobrapy
- scipy.stats (empirical p-value computation and statistical testing (Mann–Whitney U, t-test)) — https://scipy.org/
- INTEGRATE pipeline (Step 10: concordanceAnalysis.py) (implementation of FDR correction on Cohen's kappa p-values and regulatory classification) — https://github.com/qLSLab/integrate
Examples
python pipeline/concordanceAnalysis.py --valLog 1.2 --weight linear --resultsMetabolomicFile resultsMetabolomic --meansFile medie_Met.csv
Evaluation signals
- Adjusted p-values are monotonically increasing with rank (no inversions); all adjusted p-values ≥ corresponding unadjusted p-values.
- Number of reactions passing FDR < 0.05 threshold is smaller than number passing unadjusted p < 0.05; document fold-change in stringency.
- Comparison of regulatory classifications before and after FDR correction shows removal of low-concordance reactions; check that concordance metrics (Cohen's kappa) for passing reactions are elevated compared to rejected ones.
- Sanity check: for very large m (thousands of reactions), adjusted p-values inflate by factor ≈ m / rank for top hits; verify this relationship holds in output.
- Reproducibility check: re-run with identical input p-values and confirm adjusted p-values are identical and in same order.
Limitations
- Benjamini–Hochberg assumes independence or positive correlation among tests; violations (e.g., correlated fluxes in tightly coupled reactions) may reduce power or inflate FDR.
- Empirical p-values derived from randomized sampling are subject to Monte Carlo error; use sufficient sample size (typically >1000 samples per cell-line pair) to stabilize adjusted p-values.
- Single global FDR threshold (α = 0.05) may be overly stringent or permissive for reactions with low prior biological plausibility; consider sensitivity analysis or reaction-class-specific thresholds.
- When a reaction substrate is missing from metabolomics measurements, the reaction is omitted from the dataset before FDR correction, potentially biasing results toward metabolically complete pathways.
Evidence
- [other] Apply Benjamini–Hochberg FDR correction to empirical p-values derived from randomized RPS sampling to set significance threshold at FDR<5%.: "Apply Benjamini–Hochberg FDR correction to empirical p-values derived from randomized RPS sampling to set significance threshold at FDR<5%"
- [other] Compile final classification table with reaction identifiers, Cohen's kappa scores, adjusted p-values, and assigned regulatory class.: "Compile final classification table with reaction identifiers, Cohen's kappa scores, adjusted p-values, and assigned regulatory class"
- [readme] A dataset of concordance analysis (Cohen coefficient and pearson correlation) of RPS vs RAS, RPS vs FFD, RPS vs FFD, the pvalues and the adjusted pvalues: "A dataset of concordance analysis (Cohen coefficient and pearson correlation) of RPS vs RAS, RPS vs FFD, RPS vs FFD, the pvalues and the adjusted pvalues"
- [other] If one single reaction substrate is missing from the metabolomics measurements, the reaction is omitted from the dataset: "If one single reaction substrate is missing from the metabolomics measurements, the reaction is omitted from the dataset"