gabrielmoreira Version Compatibility
Reference examples tested with: R gMCP 0.8.16+, graphicalMCP 0.2+, gatekeeping, multcomp, multxpert; Python statsmodels 0.14+ for basic FDR/FWER methods.
Before using code patterns, verify installed versions match. If versions differ:
- R:
packageVersion('<pkg>')then?function_name - Python:
pip show <package>thenhelp(module.function)
If code throws ImportError, AttributeError, or TypeError, introspect the installed package and adapt the example to match the actual API rather than retrying.
Multiplicity Control for Confirmatory Trials
"Design the multiplicity strategy for my trial" -> Specify a closed-testing procedure (graphical, gatekeeping, hierarchical, or step-down Bonferroni-Holm) that controls family-wise error rate at the trial-wide level across primary endpoints, key secondary endpoints, and subgroup analyses, with provable strong FWER control.
The Foundational Theorem -- Closed Testing Is Necessary
Marcus, Peritz & Gabriel 1976 Biometrika 63:655: a hypothesis H_I (I ⊆ {1,...,m}) is rejected iff every intersection hypothesis ∩_{J⊇I} H_J is rejected by a valid α-level local test. Strong FWER control holds for ANY choice of local tests.
Goeman, Hemerik & Solari 2021 Ann Stat 49:1218 tightens this: closed testing is not merely sufficient — it is necessary for admissibility under FDP/FWER/k-FWER. Every admissible multiplicity procedure is equivalent to some closed test. Graphical procedures, gatekeepers, Hommel, fixed-sequence, fallback — all are closed tests in disguise.
FWER vs FDR philosophical divide:
- FWER: P(any false positive among m tests) — regulatory standard for confirmatory inference (agency wants to bound per-trial false-positive rate)
- FDR: Expected proportion of false discoveries among rejections — exploratory standard (genomics, fMRI, biomarker screens) where many true positives expected
Confirmatory clinical trials use FWER essentially universally.
Algorithmic Taxonomy
| Procedure | Type | FWER control | Power profile | Use case |
|---|---|---|---|---|
| Bonferroni | Single-step | Yes, any dependence | Conservative; loses 30-50% power vs Hommel under positive dependence | Very small m; worst-case dependence |
| Holm 1979 | Step-down | Yes, any dependence | Better than Bonferroni; uniformly dominates | Default for any dependence pattern |
| Hochberg 1988 | Step-up | Yes under PRDS (Sarkar 1998) | Better than Holm under PRDS | Positive correlation; verify PRDS |
| Hommel 1988 | Step-up via closed tests | Yes under PRDS | Uniformly dominates Hochberg by 1-3% | Whenever Hochberg is valid |
| Fixed-sequence (hierarchical) | Sequential | Yes, any dependence | Full alpha for first; subsequent zero if any fail | When clear priority ordering; "key secondary" labelling |
| Parallel gatekeeping (Dmitrienko 2003) | Multi-family | Yes | Family-by-family; secondary tested if any primary rejects | Primary family + secondary family |
| Serial gatekeeping | Sequential families | Yes | Strict: family k tested only if ALL of family k-1 reject | Co-primary + secondary tiers |
| Mixed gatekeeping (Dmitrienko-Tamhane 2008) | Combination | Yes | Combines closed-testing local procedures across families | Complex hierarchies |
| Graphical procedures (Bretz-Maurer 2009) | Closed-test as directed graph | Yes by construction | Flexible; allocate alpha to hypotheses via graph weights | Modern standard for confirmatory SAPs |
| Graphical + Simes/parametric (Bretz et al 2011) | Closed-test with non-Bonferroni local tests | Yes when Simes valid | Gains power under correlation | Complex co-primary + key secondary + subgroup hierarchies |
| Maurer-Bretz 2013 entangled graphs | Memory-augmented graphs | Yes by construction | Alpha propagation depends on origin | Parent-descendant constraints |
| Benjamini-Hochberg 1995 | FDR | FDR controlled at level q | Higher power than FWER | Exploratory only; NOT for confirmatory regulatory |
Postdoc reading list:
- Marcus R, Peritz E, Gabriel KR 1976 Biometrika 63:655 (closed testing — the foundation)
- Goeman JJ, Hemerik J, Solari A 2021 Ann Stat 49:1218 (closed testing necessary for admissibility)
- Holm S 1979 Scand J Stat 6:65 (step-down Bonferroni)
- Hochberg Y 1988 Biometrika 75:800 (step-up Simes)
- Hommel G 1988 Biometrika 75:383 (closed Simes; dominates Hochberg)
- Sarkar SK 1998/2008 Ann Stat (PRDS for Hochberg validity)
- Bretz F, Maurer W, Brannath W, Posch M 2009 Stat Med 28:586 (graphical procedures — foundational paper)
- Bretz F, Posch K, Glimm E, Klinglmueller F, Maurer W, Rohmeyer K 2011 Biom J 53:894 (Simes/parametric extensions)
- Maurer W, Bretz F 2013 Stat Med 32:1739 (entangled graphs / memory)
- Dmitrienko A, Offen WW, Westfall PH 2003 Stat Med 22:2387 (parallel gatekeeping)
- Dmitrienko A, Tamhane AC, Wiens B 2008 Biom J (mixed/multistage gatekeeping)
- FDA 2022 Multiple Endpoints in Clinical Trials Final Guidance (October 2022)
- Pocock SJ, Ariti CA, Collier TJ, Wang D 2012 Eur Heart J (win-ratio)
Decision Tree by Scenario
| Scenario | Recommended procedure | Why |
|---|---|---|
| 2 co-primary endpoints (both must succeed) | No alpha split needed; per-endpoint alpha-level test; cite FDA 2022 | Co-primary doesn't split alpha; inflates n via joint power |
| 2 multiple primary endpoints (any-wins) | Graphical procedure or Holm with weights | Alpha must be allocated; graphical is flexible |
| 1 primary + 2 key secondary endpoints | Hierarchical (serial gatekeeping) OR graphical with alpha propagation | Modern SAPs favour graphical |
| 1 primary + 3 secondary + 4 subgroup analyses | Graphical procedure via gMCP with pre-specified weights | Complex hierarchies benefit from graph visualisation |
| Primary endpoint + tipping-point sensitivity | No multiplicity adjustment needed for sensitivity | Sensitivity is "what if" not "another claim" |
| Many exploratory biomarker subgroups | Benjamini-Hochberg FDR | Exploratory; not for label claims |
| Win-ratio composite (cardiology) | Single test; no multiplicity | Composite captures multiple events in single hierarchy |
| Subgroup analysis (pre-specified) | Graphical alpha allocation; small budget (≤20%) per Dane 2019 | Confirmatory subgroup discovery requires explicit allocation |
| Adaptive trial with treatment arm dropping | Combination tests (Bauer-Köhne 1994) + closed testing | See clinical-biostatistics/adaptive-designs |
| Group-sequential with multiple endpoints | gsDesign or rpact with multivariate alpha spending | Hierarchical alpha across both time and endpoints |
Bretz-Maurer Graphical Procedures -- The Modern Standard
The Bretz-Maurer-Brannath-Posch 2009 Stat Med 28:586 framework recast weighted Bonferroni-Holm closed tests as directed weighted graphs:
- Vertices = elementary null hypotheses with local weights summing to 1
- Directed edges = alpha-propagation rule (when a hypothesis is rejected, its weight redistributes to descendants per edge weights)
- The graph IS the procedure: a single visual fully specifies a closed-test procedure across primary, key secondary, and subgroup hierarchies
gMCP R package
library(gMCP)
# Construct a graph for primary + 2 key secondary endpoints
# Primary endpoint at full alpha; if rejected, alpha propagates equally to secondaries
hypotheses <- c('Primary', 'Sec1', 'Sec2')
weights <- c(1, 0, 0) # initial alpha all on primary
# Transition matrix: rows = source, columns = target
# When Primary rejects, weight 0.5 goes to each secondary; when Sec1/Sec2 rejects, alpha returns
transitions <- matrix(c(
0, 0.5, 0.5,
0, 0, 1,
0, 1, 0
), nrow = 3, byrow = TRUE, dimnames = list(hypotheses, hypotheses))
graph <- graphMCP(m = transitions, weights = weights, hnames = hypotheses)
# Note: in current gMCP, the graph constructor is `graphMCP(m=, weights=, hnames=)`;
# `matrix2graph()` appeared in older tutorials and is not the canonical exported API
# -- verify with `?graphMCP` / `?gMCP` in the installed gMCP release before scripting.
# Set p-values from the trial
p_vals <- c(Primary = 0.018, Sec1 = 0.042, Sec2 = 0.038)
# Run the graphical procedure at alpha = 0.025
result <- gMCP(graph, pvalues = p_vals, alpha = 0.025)
print(result)
# Hierarchical rejection: Primary rejects -> alpha propagates to secondaries -> ...
Standard SAP graph patterns
| Pattern | Graph topology | Use |
|---|---|---|
| Pure hierarchical (fixed sequence) | H1 → H2 → H3 with weight 1 on each transition | Strict ordering |
| Holm graph (equal weights) | Each Hi → Hj with weight 1/(m-1) | No priority ordering |
| Primary + secondaries | Primary → Sec1 (0.5), Sec2 (0.5); Sec1 ↔ Sec2 (1) | Pivotal labeling claims |
| Co-primary chain | H1 → H2 with full weight if BOTH H1a, H1b reject | Co-primary + secondary |
| Subgroup branch | Primary → Subgroup_OS (0.2), Sec1 (0.4), Sec2 (0.4) | Discovery subgroup with budget |
Bretz et al 2011 -- Simes and parametric extensions
When endpoints are positively correlated, replace the Bonferroni-based intersection test with Simes (for positive dependence) or parametric (using known correlation):
library(gMCP)
# Use Simes-based local tests at each intersection
result_simes <- gMCP(graph, pvalues = p_vals, alpha = 0.025, test = 'Simes')
# Or parametric with estimated correlation matrix
result_param <- gMCP(graph, pvalues = p_vals, alpha = 0.025, corr = correlation_matrix)
Maurer-Bretz 2013 entangled graphs
Entangled graphs add memory: the alpha propagation can depend on the origin of the alpha. This allows parent-descendant constraints that a single non-entangled graph cannot express. Example: secondary endpoint Sec1 receives alpha only from Primary, never from Sec2.
Postdoc argument: purists argue memory makes the procedure non-coherent in Gabriel's sense; Glimm/Maurer/Bretz argue it matches real-world inferential intent.
Gabriel coherence in plain terms: a coherent procedure rejects a hypothesis H consistently regardless of which superset of H is being tested. Non-entangled graphs are coherent: if H1 is rejected via path A, it would also be rejected via path B. Entangled (memory-bearing) graphs sacrifice coherence: the same H may be rejected when alpha arrives from one parent but not from another, because the propagation history changes the available alpha. The trade-off is operational power -- entangled graphs can encode "secondary X is meaningful only if primary Y rejects, not if primary Z rejects" inferential intent that flat coherent procedures cannot express. Choose based on whether the SAP needs path-dependent priority.
Gatekeeping Procedures
Serial gatekeeping (hierarchical)
Test H1 at full alpha; only if it rejects, test H2 at full alpha; etc. Maximises power for H1 but H_k becomes inferentially worthless once any H_j (j<k) fails.
# Hierarchical / serial: just a chain graph in gMCP
hyp <- c('H1', 'H2', 'H3', 'H4')
weights <- c(1, 0, 0, 0)
trans <- matrix(c(0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0, 0, 0, 0),
nrow=4, dimnames=list(hyp, hyp))
graph <- graphMCP(m = trans, weights = weights, hnames = hyp)
Pre-specification of order is critical — based on clinical importance, NOT expected effect size. Ordering by expected effect is data-driven and inflates Type-I.
Parallel gatekeeping (Dmitrienko 2003)
Secondary family is tested only if at least one primary rejects. Bonferroni-based parallel gatekeeper has stepwise representation (Guilbaud 2007 Biom J 49:917).
Mixed / multistage (Dmitrienko-Tamhane 2008)
Permits using any closed-testing local procedure (e.g., Holm in family 1, Hommel in family 2) and combining via closure principle. R gMCP::generalMixGatekeeping or Mediana/MultXpert packages.
Postdoc tradeoff: parallel gatekeeping power loss vs collapsing endpoints into a composite (which avoids multiplicity but dilutes effect if components move in opposite directions); whether tree gatekeeping (Dmitrienko 2008 Stat Med 27:2114) over-engineers vs equivalent graphical procedure.
Hochberg vs Hommel vs Holm
Holm 1979 — step-down rejective Bonferroni; FWER controlled under any joint dependence. Conservative but robust.
Hochberg 1988 — step-up using ordered Simes critical values; needs Simes inequality which requires PRDS (Sarkar 1998, 2008). Under PRDS, Hochberg uniformly dominates Holm.
Hommel 1988 — also Simes-based but uses closed-testing tableau directly (not step-up shortcut). Uniformly more powerful than Hochberg (typically 1-3% gain).
When Hochberg fails (anti-conservative)
Hochberg becomes Type-I-inflated under negative dependence — relevant when comparing endpoints mathematically constrained to move in opposite directions (LDL-C and HDL-C; complementary efficacy and safety endpoints).
Sarkar critique: when PRDS cannot be proven, fall back to Holm. The lost power is the price of robustness.
# Python: statsmodels supports Holm, Hochberg, Hommel
from statsmodels.stats.multitest import multipletests
p_vals = [0.018, 0.042, 0.038, 0.015]
for method in ['holm', 'hochberg', 'hommel', 'bonferroni']:
reject, adj_p, _, _ = multipletests(p_vals, alpha=0.05, method=method)
print(f'{method}: reject={reject}, adjusted={adj_p}')
FDA Multiple Endpoints Final Guidance (October 2022)
Federal Register 2022-22882 finalises 2017 draft. Key changes vs draft:
- Explicit recognition of newer methods including win-ratio (Pocock 2012 Eur Heart J) and weighted composites
- Clearer language that "key secondary" endpoints are those for which sponsor wishes to make label claims and which must be in a Type-I-error-controlled hierarchy
- Appendix with worked graphical-procedure examples
Categories
| Category | Approach | Note |
|---|---|---|
| Composite | Single test; no multiplicity | Win-ratio, DOOR/RADAR, time-to-first-event |
| Co-primary (all-win) | Each at full alpha; n inflated for joint power | Power = product of marginals |
| Multiple primary (any-wins) | Alpha must be split (Bonferroni or graphical) | More n required than co-primary if effects similar |
| Primary + key secondary | Hierarchical or graphical | Modern preference: graphical for flexibility |
Winner's bias warning: when post-hoc-selected endpoints are emphasised, bias-corrected effect estimates are recommended (same selection-bias issue as adaptive design).
The "Almighty Primary Endpoint" Critique
Dmitrienko-D'Agostino 2017 Stat Med 36:4341 editorial + 2024 Pharm Stat discussion: the dogma of a single primary endpoint causes systematic Type-II error inflation in trials with broad multi-domain benefit (heart failure drugs with effects on mortality, hospitalisation, symptoms, biomarkers).
Win-ratio (Pocock-Ariti-Collier-Wang 2012) and hierarchical composite (DOOR/RADAR, Evans 2015) are responses — they preserve a single inferential test while letting multiple endpoints contribute.
FDA counter-position (Hung, O'Neill, Wang): without a designated primary, sponsors and regulators negotiate over secondary endpoints post hoc, destroying inferential meaning. Hence the FDA 2022 guidance reaffirms key-secondary hierarchies.
Per-Method Failure Modes
Hochberg under negative dependence
- Trigger: Endpoints constrained to move in opposite directions (LDL vs HDL; efficacy vs harm).
- Mechanism: Hochberg's PRDS assumption fails; Simes inequality doesn't hold; Type-I inflated.
- Symptom: Replication with Holm finds non-significant where Hochberg rejected.
- Fix: Switch to Holm (no PRDS assumption); cite Sarkar 1998.
Fixed-sequence with wrong ordering
- Trigger: Ordering by expected effect size rather than clinical priority.
- Mechanism: Data-driven ordering inflates Type-I.
- Symptom: Reviewer asks for pre-specified ordering rationale.
- Fix: Pre-specify order by clinical priority in SAP; document rationale.
Graphical procedure without pre-specified weights
- Trigger: Weights chosen at analysis time to favour observed results.
- Mechanism: Equivalent to post-hoc multiplicity tuning; inflates Type-I.
- Symptom: Multiple "what if" graph variants in CSR.
- Fix: Pre-specify graph and weights in SAP; document at protocol design.
Bonferroni when graph would gain power
- Trigger: Default conservative choice when no thought put into structure.
- Mechanism: Loses 30-50% power vs Hommel/graphical when m ~ 10 correlated tests.
- Symptom: Underpowered trial reaches non-significance where graphical procedure would.
- Fix: Design a proper graph in
gMCP; cite Bretz-Maurer 2009.
FDR used for confirmatory primary
- Trigger: SAP specifies BH-FDR for primary multiplicity.
- Mechanism: FDR controls expected proportion of false discoveries, not P(any false positive).
- Symptom: Regulatory reviewer rejects as non-confirmatory.
- Fix: FWER (graphical, Holm, Hochberg, Hommel) for confirmatory; FDR for exploratory only.
Subgroup analyses claimed without multiplicity
- Trigger: Trial reports 10 subgroups with one significant at α=0.05.
- Mechanism: ~40% probability of at least one false positive under global null.
- Symptom: Cherry-picked subgroup claim in submission.
- Fix: Pre-specified graphical alpha allocation OR explicit hypothesis-generating label; cite EMA 2019 subgroup guideline.
Win-ratio reported without hierarchical priority
- Trigger: Win-ratio composite with unspecified component priority.
- Mechanism: Component prioritisation drives the result; arbitrary choice = data-dependent answer.
- Symptom: Two analysts get different results from same data depending on hierarchy.
- Fix: Pre-specify hierarchy in SAP; sensitivity over alternative hierarchies.
Quantitative Thresholds
| Threshold | Source | Rationale |
|---|---|---|
| FWER for confirmatory; FDR for exploratory | ICH E9; FDA 2022 Multiple Endpoints | Regulatory standard universally |
| Bonferroni: ~10 tests -> 30-50% power loss | Sarkar 1998 PRDS | Conservative under positive dependence |
| PRDS required for Hochberg validity | Sarkar 2008 Ann Stat | Otherwise Type-I inflated; fall back to Holm |
| Subgroup α budget <=20% of total | Dane 2019 EFSPI white paper | Discipline against subgroup fishing |
| Key secondary requires hierarchy in SAP | FDA 2022 Final | Labeling claims need Type-I-controlled test |
| Composite avoids multiplicity but dilutes effect | Pocock 2012 Eur Heart J | Win-ratio captures heterogeneity in single test |
Common Errors
| Error / symptom | Cause | Solution |
|---|---|---|
| Hochberg applied to negatively-dependent endpoints | PRDS not checked | Switch to Holm (cite Sarkar 1998) |
| Fixed-sequence ordering data-driven | Post-hoc selection | Pre-specify clinical priority in SAP |
| Bonferroni at 10 correlated endpoints | Default conservatism | Graphical procedure (gMCP); 30-50% power gain |
| FDR for confirmatory primary | Misunderstanding error rates | FWER mandatory for confirmatory; FDR exploratory only |
| Graphical procedure run with multiple weight schemes | Post-hoc graph tuning | Pre-specify single graph in SAP |
| Subgroups significant without multiplicity | Cherry-picking | Pre-specified allocation OR explicit hypothesis-generating label |
| Co-primary treated as multiple primary | Confused alpha allocation | Co-primary: no alpha split; inflate n. Multiple primary: split alpha |
| Win-ratio component priority unspecified | Data-driven choice | Pre-specify hierarchy with rationale; sensitivity over alternatives |
multipletests default method='hs' (Holm-Sidak) |
Common Python mistake | Always specify method='holm', 'hommel', etc., explicitly |
| Sensitivity analysis listed as a "key secondary" requiring alpha | Confusion about role | Sensitivity is "what if" not "another claim"; no alpha needed |
Anticipated Reviewer Pushback
| Pushback | Response |
|---|---|
| "Why this multiplicity procedure?" | Closed testing per Marcus-Peritz-Gabriel; specific implementation is graphical (Bretz-Maurer 2009) with pre-specified weights in SAP |
| "Why Hommel not Holm?" | PRDS holds (positive correlation among endpoints); Hommel dominates Holm by 1-3% with no Type-I cost |
| "Why graph weights X, Y, Z?" | Clinical priority: primary > key secondary > exploratory; weights reflect labelling claim hierarchy |
| "Are these endpoints positively correlated?" | Sensitivity analyses provided: Bonferroni, Holm, Hochberg, Hommel results all in CSR appendix; concordant |
| "Where is alpha for the subgroup analysis?" | Pre-specified 20% of primary alpha allocated; cite Dane 2019 |
| "Why not just composite endpoint?" | Composite would dilute differential effect on mortality vs hospitalisation; key-secondary hierarchy preserves component-level claims |
| "PRDS check for Hochberg?" | Endpoints positively correlated via simulation under null; PRDS holds; Hochberg/Hommel valid |
| "Sensitivity in the hierarchy?" | No — sensitivity is "what if" and does not require alpha. Listed as supportive not key secondary. |
References
- Bretz F, Maurer W, Brannath W, Posch M. 2009. A graphical approach to sequentially rejective multiple test procedures. Stat Med 28:586-604.
- Bretz F, Posch K, Glimm E, Klinglmueller F, Maurer W, Rohmeyer K. 2011. Graphical approaches for multiple comparison procedures using weighted Bonferroni, Simes, or parametric tests. Biom J 53:894-913.
- Burman CF, Sonesson C, Guilbaud O. 2009. A recycling framework for the construction of Bonferroni-based multiple tests. Stat Med 28:739-761.
- Dmitrienko A, Offen WW, Westfall PH. 2003. Gatekeeping strategies for clinical trials that do not require all primary effects to be significant. Stat Med 22:2387-2400.
- Dmitrienko A, Tamhane AC, Wiens BL. 2008. General multistage gatekeeping procedures. Biom J 50:667-677.
- FDA. 2022. Multiple Endpoints in Clinical Trials. Final Guidance.
- Goeman JJ, Hemerik J, Solari A. 2021. Only closed testing procedures are admissible for controlling false discovery proportions. Ann Stat 49:1218-1238.
- Guilbaud O. 2007. Bonferroni parallel gatekeeping -- transparent generalizations, adjusted p-values, and short proofs. Biom J 49:917-927.
- Hochberg Y. 1988. A sharper Bonferroni procedure for multiple tests of significance. Biometrika 75:800-802.
- Holm S. 1979. A simple sequentially rejective multiple test procedure. Scand J Stat 6:65-70.
- Hommel G. 1988. A stagewise rejective multiple test procedure based on a modified Bonferroni test. Biometrika 75:383-386.
- Marcus R, Peritz E, Gabriel KR. 1976. On closed testing procedures with special reference to ordered analysis of variance. Biometrika 63:655-660.
- Maurer W, Bretz F. 2013. A graphical approach to multiple testing in clinical trials with simultaneous testing of multiple hypotheses. Stat Med 32:1739-1753.
- Pocock SJ, Ariti CA, Collier TJ, Wang D. 2012. The win ratio: a new approach to the analysis of composite endpoints in clinical trials. Eur Heart J 33:176-182.
- Sarkar SK. 2008. Generalizing Simes' test and Hochberg's stepup procedure. Ann Stat 36:337-363.
Related Skills
- clinical-biostatistics/trial-reporting - Multiplicity strategy reporting per CONSORT 2025
- clinical-biostatistics/subgroup-analysis - Subgroup multiplicity allocation
- clinical-biostatistics/power-and-sample-size - Power adjustment for co-primary endpoints
- clinical-biostatistics/adaptive-designs - Combination tests for adaptive multiplicity
- clinical-biostatistics/effect-measures - Reporting multiple effect measures post-multiplicity adjustment
- experimental-design/multiple-testing - General methods (FDR, FWER, q-values)