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Incomplete references leave bulk deconvolution targets non-identifiable, but identification has a computable precision price

涵宇 蒋iD, Fei Gao, Peixi Liu, Yaheng Wu, Ying JieiD, Ying LiiD, Yang Jiang

Abstract

Background. Reference-based deconvolution estimates cell-type proportions from bulk profiles. Incomplete references compromise these estimates, yet many remedies return point estimates. We separate the operator provenance that reproduces an estimate from the information and precision that identify its target. Results. Two operator histories at one reduced reference give different estimators: 28.2% of 196,420 sample-deletion pairs differed by >0.1 total variation; locking every learned component made paths identical. Across nine cohorts, operator history reversed 160 of 952 association signs, 31 with a significant path, and changed significance for 126. Observationally equivalent completions can fill the open simplex and reverse retained-type rankings. Under a joint zero-exposure condition, shared structure leaves inherited bounds unchanged; one to six uncalibrated views also gave identical bounds. A profile library contracted estimator-output envelopes by 98.93% yet covered the full-reference effect for 42.77%, with 19 wrong-sign certificates; conditional sharp bounds stayed at [-1, 1]. Treating RNA yields as exact collapsed intervals to points covering none of seven flow-measured targets: contraction without coverage is false certainty. Calibrated cross-modal anchors contract width to 0.51 at six types but certify no valid sign. Exact RNA yields identify cell fractions from RNA contributions; a decisive sign in blood requires {+/-}2.6% proxy accuracy with near-total contraction of donor-heterogeneity and dynamic-range envelopes. Conclusions. Incomplete-reference deconvolution is an identification problem, not only an estimation problem. Remedies must be scored on shrinkage, coverage, certification and false certification against held-out targets. fitdrop implements this scoring and a precision frontier for planning decisive measurements.

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In-depth summary

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Claude Opus 5.5 · xhigh effort · 8 Nov 2026 · from the full text of version 2 (18 Sept 2026) · CC BY 4.0

With an incomplete deconvolution reference, operator history changes estimates and associations, and the target is not point-identified; fitdrop scores remedies on shrinkage, coverage, certification and false certification, and prices measurements.

Methods that handle cell types missing from a deconvolution reference return point estimates, and earlier deletion studies mix the column removal with re-learning of the measurement operator in mostly unreported proportions. The authors report no earlier formal analysis of the identified set for the retained-composition target, and no study crossing fully frozen with fully rebuilt operator states at a fixed terminal reference.

Key results

  1. ShownOn an identical reduced reference and bulk, carrying operator state learned on the full reference (frozen) versus re-learning it (refit) yields different compositions, attributable solely to re-learned state; neither path is consistently closer to orthogonal imaging truth.

    Frozen-refit total-variation distance exceeded 0.1 for 28.2% of 196,420 sample-deletion pairs; locking all learned components gave zero difference in 32 of 32 conditions. Against Huuki-Myers RNAScope/immunofluorescence composition, 13 of 24 prespecified contrasts excluded zero (10 frozen, 3 refit); astrocyte deletion favored frozen for Bisque in the Total×RiboZeroGold stratum (+0.044, 90% CI 0.035 to 0.050). · Fitting and deleting do not commute; Against orthogonal measurement, path advantage…; Estimators and operator states; Imaging-benchmark evaluation (Huuki-Myers DLPFC)

  2. ShownSwitching operator history alone reverses the sign and significance of associations between estimated proportions and disease phenotypes in real cohorts, by amounts comparable to or larger than sampling error.

    In nine cohorts, 160 of 952 frozen/refit association pairs had opposite signs (31 with a significant path) and 126 changed significance; monocyte/macrophage vs COVID-19 was positive on frozen (FDR = 0.030) and negative on refit (FDR = 0.006); 220 of 952 between-path 95% intervals excluded zero; over 392 pairs, median |Δβ| was 0.52 times the frozen-path standard error (3.9 at the 90th percentile). · Operator history reverses cohort associations; Real-cohort associations; Between-path inference in real cohorts

  3. ShownEven with the operator fixed, the observed bulk and incomplete reference do not point-identify the retained-type composition: at an explicit observation, exact completions realize every retained composition in the open simplex, and no observed-data rule picks the closer history uniformly.

    Exact witness (3 features, 2 retained types): two completions reproduce the bulk exactly yet give (3/5, 2/5) vs (3/10, 7/10). Theorem 1 extends this to the whole open simplex (condition number at most 1313/485); Theorem 2 gives minimax regret δ = 3/10 for deterministic selectors; 80 exact checks. Five diagnostics had AUC 0.445 to 0.574 for picking the lower-error path in 400 synthetic dictionary instances. · The full-reference target is not…; Synthetic deletion spectrum; Two-completion witness and theorems

  4. ShownAdding uncalibrated views, finite profile libraries or exact RNA yields either leaves the identified set unchanged or narrows outputs while losing coverage; calibrated cross-modal anchors narrow width with coverage but yield no valid sign certificate.

    Uncalibrated views (one to six preparations) gave identical width 1.0000. Profile library: 98.93% contraction, 42.77% coverage of the full-reference effect (355/830), 19 wrong-sign certificates; conditional sharp bounds stayed [−1, 1]. Exact RNA yields covered 0 of 7 flow targets (CIBERSORT false certification 71.43%). Six anchored types cut width to 0.5067; none of 231 grid cells met both thresholds. · Proposition (shared completion structure); Contraction without coverage is false certainty; Three ceilings, and the measurement frontier; Multi-view and anchor analyses (Huuki-Myers)

  5. SuggestedInverting the prespecified uncertainty model prices a decisive measurement: in blood, fixing the sign of T-cell fraction minus RNA contribution needs near-point joint precision, and direct mRNA-per-cell measurement across donors ranks ahead of deeper sequencing.

    Along the prespecified equal joint-scaling path, the sign requires total-RNA-to-mRNA proxy error within ±2.6% while 97.4% of the log-scale donor-heterogeneity and dynamic-range envelopes is removed; Shapley width shares: 60.1% donor/leaf heterogeneity, 33.6% proxy, 6.3% dynamic range; non-negative least squares (NNLS) needs a modeled 151, 381 and 25,168 donors at 0%, 2% and 5% systematic error, none at 10%. · Three ceilings, and the measurement frontier; A measurement contract, and what it costs to…; Precision inversion (absolute scale)

Methods, data and reproducibility

Each deletion ran twice on the same reduced reference and bulk (frozen full-reference operator state vs refit) for five estimators in four tissues, against imaging, flow, constructed and cohort benchmarks; exact theorems and linear-programming feasible-set bounds scored remedies on shrinkage, coverage, certification and false certification, and uncertainty models were inverted into precision requirements.

  • Huuki-Myers dorsolateral prefrontal cortex (DLPFC) resource: bulk RNA-seq across six library preparations, donor-matched snRNA-seq reference (56,447 nuclei), RNAScope/IF block-level composition · human · n = 110 bulk libraries; 19 tissue blocks; 10 donors
  • Primary disease cohorts for association analyses: lung (two platforms), whole-blood leukocyte (COVID-19 status) and cornea (discovery/replication split) · n = 474, 126 and 50 samples · GSE47460; GSE157103; GSE77938
  • Additional cohorts admitted by two-stage screening of the 23 remaining cohorts (GSE166190 longitudinal, supplementary only) · n = seven cohorts · GSE112155; GSE102556; GSE102741; GSE174409; GSE68719; GSE166190; GSE171110
  • Blood-cell mixtures of peripheral blood mononuclear cells (PBMC) with 3 to 6% admixed granulocytes, with matched flow cytometry · n = nine samples · GSE107572
  • PBMC bulk RNA-seq with flow proportions (29 flow leaves mapped to seven reference compartments) · n = 13 samples (12 with matched flow) · GSE107011
  • Whole-blood DNA methylation test set with flow-measured proportions, for IDOL-based deconvolution · n = six samples (36 sample-deletion units)
  • Allen Institute DLPFC atlas (region label DFC), restricted to a six-type common core for cross-atlas transfer
  • Constructed Dirichlet pseudo-mixtures from held-out reference cells (PBMC, lung, DLPFC) and a synthetic deletion spectrum · n = 1,500 mixtures per tissue; 400 dictionary instances
Methods & tools
fitdrop 0.2.0 (R package, incl. precision_frontier), BisqueRNA 1.0.5, MuSiC 1.0.0, SCDC, NNLS, CIBERSORT (authors' nu-support-vector regression re-implementation), IDOL (DNA methylation library selection), SciPy linprog (HiGHS dual simplex), RNAScope/IF imaging, flow cytometry, snRNA-seq
Software & environment
fitdrop 0.2.0 R package (passes R CMD check; tests recover the vignette headline numbers); BisqueRNA 1.0.5, MuSiC 1.0.0; SciPy linprog (highs-ds); an independent re-execution reproduced all 54 reported quantities.
Reproducibility gaps
CIBERSORT results come from a re-implementation without the official quantile normalization; the full accession list (including the Huuki-Myers resource, the Allen atlas and the DNA-methylation test set) is only in Supplementary Table S1; no hardware, runtime or container is described.
Limitations (6)
  • Each imaging probe panel labels only three of six broad types, so composition is conditional within panels, and the resource's authors caution that deconvolution may track RNA contribution; under cell-size weighting all four headline path-contrast intervals cross zero. · stated by the authors
  • The flow-sorted RNA benchmark has only nine samples, and flow measures cell fractions whereas deconvolution without cell-size correction estimates RNA-mass fractions. · stated by the authors
  • The SVR-based estimator labelled CIBERSORT is the authors' re-implementation without quantile normalization, so its results need not carry over to the official distribution. · stated by the authors
  • Cohort association tests were not adjusted for covariates, and the repeated-draw cohort GSE166190 was kept out of primary family-level inference. · stated by the authors
  • The shared-structure pilot covers one PBMC panel and left 107 of 384 optimization extrema unresolved, including all 36 main-profile extrema of the rank-one class, so real-data support for the Proposition is partial. · noted in this summary
  • Precision prices rest on 12 PBMC donors and one anchor resource (7 blocks, 6 donors), and donor counts are modeled under independence and fixed-variance assumptions, so they are planning estimates rather than validated requirements. · noted in this summary

Who should read:Read this if you report, compare or regress cell-type proportions from reference-based bulk deconvolution when the reference lacks or edits cell types, or if you build methods that recover missing types.

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