REVIEW 2 major objections 4 minor 43 references
Group Testing with Selectable Thresholds
T0 review · 2 major / 4 minor · reviewed 2026-08-02 · deepseek-v4-flash
Pith's one-line read This paper shows that letting each pooled test choose its own positive threshold lets non-adaptive group testing reach the maximum possible rate of one bit per test when the threshold is unbounded.
desk verdict New model and a likely-solid converse, but Theorem 4's achievability rests on a COMP/DD claim that does not hold at the stated test count. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The two-batch algorithm is the central construction: batch one uses standard threshold-1 group testing (COMP/DD, or a SUBSET subroutine in the unbounded case) to find a set S_DD of k(1-o(1)) defectives plus a superset containing all defectives; batch two runs near-constant-column-weight tests at threshold gamma_max, and an item is 'resolved' by a test containing exactly gamma_max-1 items from S_DD and no other uncertain item. The probability of such a test is asymptotically Poisson, nu^{gamma_max-1} e^{-nu}/(gamma_max-1)!, which produces the explicit denominator in the rate formula. The converse rests on the masking mechanism: an item is masked when no test is informative for it (contains it
What would settle it
Run the fixed-gamma_max two-batch algorithm for gamma_max=2 with n=10^6 and k=n^0.95, sweep T around the predicted value, and check whether empirical error probability drops to zero at the predicted (1/log 2) k log2(n/k) + k log k / 0.636 tests; a mismatch would falsify Theorem 4, while agreement would support the claim that selectable thresholds strictly beat standard group testing in the dense regime.
Extended reading notes
Core claim
The paper's central claim is that making the threshold a selectable parameter turns threshold group testing into a problem whose information-theoretic rate can reach 1 when gamma_max is unbounded, and whose fixed-threshold rate is characterized by matching achievability and converse bounds in the dense limit. The constructive idea is a two-batch scheme: first use ordinary threshold-1 group testing to identify a near-complete set of defectives, then use tests with threshold gamma_max to resolve the remaining uncertain items; the fixed-threshold analysis shows the second batch needs k log k / [nu log(1/(1 - nu^{gamma_max-1} e^{-nu}/(gamma_max-1)!))] tests. On the converse side, the paper prove
Load-bearing premise
The rate-1 and large-gamma_max achievability claims rest on a cited SUBSET subroutine that the paper flags as only proved for a computationally inefficient method, and the matching converse additionally assumes near-constant test sizes/degrees with bounded overlaps; if either premise gives way, the corresponding headline results remain conditional.
Editorial extensions
If this is right
- With unbounded selectable thresholds, T = k log2(n/k)(1+o(1)) tests suffice for non-adaptive recovery, matching the counting bound and making the rate exactly 1.
- For fixed gamma_max, the two-batch algorithm runs in polynomial time and uses (1/log 2) k log2(n/k) + min_nu k log k / [nu log(1/(1 - nu^{gamma_max-1} e^{-nu}/(gamma_max-1)!))] (1+o(1)) tests.
- As gamma_max grows, the achievable rate approaches 1 at least as fast as 1 - O(1/sqrt(gamma_max)), and the converse shows the k log k coefficient cannot decay faster than 1/sqrt(gamma_max).
- In the dense limit theta -> 1, achievability and converse for fixed gamma_max have matching k log k coefficient, so the number of tests is determined to within o(k log k).
- Information-theoretically, selectable thresholds do not beat just using the largest threshold; their value is algorithmic simplicity.
Reading between the lines
- The two-batch template suggests a general recipe: any standard group-testing method that returns a near-complete defective set can be upgraded with high-threshold resolution tests, and nothing in the analysis appears to require exactly two batches.
- Because the converse assumes near-constant weights/degrees and bounded overlaps, the picture for non-regular designs such as Bernoulli-type test matrices is open; a numerical study in the dense limit would show whether the matched k log k coefficient survives without those regularity conditions.
- The proven rates use only thresholds 1 and gamma_max; a natural testable extension is whether intermediate thresholds close the remaining gap for fixed theta < 1, although the paper's Lemma 1 suggests no information-theoretic gain from them.
- For applications with noisy threshold devices, the idealized exact-threshold model would need calibration, and the second batch's reliance on exact counts of gamma_max-1 known defectives suggests a noise sensitivity that could be probed by simulation.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces selectable-threshold group testing (GT-ST): each binary pooled test can be assigned its own threshold γ(t) ≤ γmax, with outcome 1{ψ_t ≥ γ(t)}. The authors prove the counting bound; show rate 1 is achievable when γmax is unbounded (Theorem 2) and rate 1−O(γmax^{-1/2}) for large γmax (Theorem 3), both by a two-batch strategy built on the SUBSET result of [22]; give a finite-γmax achievability result with polynomial-time COMP/DD decoding (Theorem 4); and prove masking-based converses (Theorems 5 and 6) under near-constant weight/degree and bounded-overlap assumptions, with an optimization lemma showing that the converse is dominated by the largest threshold. The proofs are detailed and the exposition is careful.
Significance. If its results held, the paper would be a valuable contribution: it formulates a natural generalization of threshold group testing, gives simple rate-1 constructions in the unbounded/large-threshold regime (modulo the acknowledged external SUBSET subroutine), and provides a converse that is more general than concurrent work. The masking-based proof is sophisticated and mostly internally consistent, and the authors are explicit about assumptions and external dependencies. However, the central finite-γmax achievability theorem is unsupported as written because the batch-1 COMP/DD guarantee is quantitatively false at the stated test count; this directly undermines Eq. (11) and the claimed comparison with standard GT.
major comments (2)
- [App. B-C, Theorem 4, Eq. (11)] The batch-1 claim that COMP produces S_COMP of size k(1+o(1)) is not a valid consequence of [22, App. D] and is contradicted by the authors' own parameters. With T1=(1/log2)k log2(n/k) and L1=T1 log2/k=log2(n/k), the effective inclusion probability is p=L1/T1=log2/k. For a fixed non-defective, a test is negative with probability (1-p)^k→1/2, so the expected number of negative tests containing the item is T1·p/2=(1/2)log2(n/k). Hence P(item remains in S_COMP)=exp(−(1/2)log2(n/k))=(n/k)^{−1/(2 ln2)}≈(n/k)^{−0.721}, and E|S_COMP\S|≈n(n/k)^{−0.721}=n^{0.279+0.721θ}, which is ω(k) for every θ<1. Thus S_COMP cannot have size k(1+o(1)), and the later union bound over |S_COMP\S_DD|=o(k) is invalid.
- [Section II-C and Fig. 1] The finite-γmax claims of strict improvement over standard GT are not supported independently of the faulty batch-1 step. At the inclusion probability used in the proof, the number of batch-1 tests must be increased by a factor greater than 2ln2≈1.386 even to make the COMP false positives o(k); the DD step is also contaminated by the large false-PD set. The authors should either supply a correct batch-1 subroutine that provably meets the stated T1, or restate Theorem 4 and Figure 1 with a corrected leading term and re-evaluate the comparison.
minor comments (4)
- [Lemmas 2 and 9] The display γ^{-1/3} appears where the proof clearly means γ−1/3 (γ minus one third). Please fix the notation; as typeset it is ambiguous and initially reads as a tiny exponent.
- [App. B-C, [22, App. D]] Since [22, App. D] supplies the crucial COMP/DD guarantee for Theorem 4, the paper should state the exact lemma used, including the hypotheses and the precise sense in which S_DD and S_COMP have the claimed sizes, rather than only citing it.
- [Fig. 1] The caption should specify precisely which curve from [20] is plotted and in which metric. The current description makes the claimed comparison in the dense limit difficult to verify.
- [Theorem 3 proof] The step that discards tests whose repeated outcomes are all identical should clarify that this is valid only on the high-probability event that ψ_t lies in the interval (γ_-, γ_+); a sentence about boundary effects near γ_± would help.
Circularity Check
No significant circularity: the central derivations reduce to prior standard-GT theorems, not to their own conclusions.
full rationale
I found no step in which a claimed prediction is equivalent by construction to an input or fitted value. The strongest claims (Theorems 2 and 3) use the SUBSET subroutine from [22] ('This can be done with a number of tests meeting the counting bound [22, Thm. 2]'), and Theorem 4 uses the COMP/DD approximation guarantee from [22, App. D]. These are self-citations (McMorrow and Scarlett are co-authors), and Section I-C is transparent that the SUBSET route is 'albeit only currently proved for a computationally inefficient method'; but the cited results are about standard group testing with one-sided error, not about the selectable-threshold model of this paper. They are used as black-box subroutines, not as a restatement of the target result, so they are independent support rather than circularity. The converse (Theorems 5-6) is derived in the paper from masking and informative-test arguments under Assumptions 1-3; those assumptions are regularity conditions, not conclusions, and are checked for the NCC design in Appendix D. The optimization over nu in Theorem 4 and Delta in Theorem 6 is minimization, not data fitting, so no 'fitted input called prediction' pattern occurs. The dense-limit match between Theorem 4 and Theorem 6 arises from independently derived formulas rather than one being inserted into the other. The skeptic's numerical false-positive calculation against Theorem 4 is a potential correctness gap in a cited COMP/DD claim, but it does not exhibit a circular reduction; it alleges the cited result is wrong at the stated test count, which is a validity concern, not a self-referential derivation. Accordingly no circular step is identified.
Assumptions & free parameters
free parameters (4)
- nu (batch-2 inclusion parameter) =
optimized over nu>0; for gamma_max=2 the denominator max is numerically about 0.636
- Delta (row-weight constant in converse) =
arg max over Delta>0 of h(Delta,gamma); for large gamma, Delta* is in [gamma-1/3, gamma]
- alpha_r (fraction of tests per threshold) =
optimized over the simplex; Lemma 1 shows the maximum is attained by putting all mass on the highest threshold
- Bernoulli inclusion probabilities (log^4 k/k and gamma_max/(2k)) =
chosen per theorem: log^4 k/k for unbounded threshold, gamma_max/(2k) for large gamma_max
assumptions (6)
- domain assumption Uniform combinatorial prior on the defective set: S is uniform over all k-subsets of [n].
- domain assumption Sublinear sparsity k = Theta(n^theta) with theta in (0,1).
- domain assumption Noiseless threshold measurements: y_t = 1{psi_t >= gamma^(t)} with exactly specified thresholds.
- standard math SUBSET achievability at the counting bound from [22].
- ad hoc to paper Assumptions 1-3: near-constant item degrees and test weights, and bounded pairwise test intersections.
- standard math Standard probabilistic tools: Chernoff, McDiarmid, FKG, Poisson approximation, Stirling bounds.
Cite this review
Pith. "Pith review of Group Testing with Selectable Thresholds." pith.science (2026). https://pith.science/paper/QIF37T7Y
@misc{pith2026260714448,
author = {Pith},
title = {Pith review of: Group Testing with Selectable Thresholds},
year = {2026},
howpublished = {\url{https://pith.science/paper/QIF37T7Y}},
note = {Machine review of arXiv:2607.14448}
}
abstract
We consider the problem of group testing, in which one seeks to identify a subset of defective items of size $k$ from a larger set of $n$ items based on pooled tests. We introduce a selectable threshold model, in which each test has an associated threshold that can be chosen, such that the test outcome is 1 if and only if the number of defectives in the test is no smaller than that threshold. In settings with a large or unbounded maximum threshold, we establish conditions under which high-probability recovery can be attained with a rate (i.e., the asymptotic ratio of $\log_2{n \choose k}$ to the number of tests) approaching its maximum possible value of 1. Moreover, in the case of a fixed maximum threshold, we establish an achievable number of tests using simple and computationally efficient decoding methods, and a converse that holds under suitable regularity conditions on the test design, with the two coinciding in the dense limit (i.e., $\theta$ approaching one in the scaling $k = \Theta(n^{\theta})$).
Figures
Reference graph
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