REVIEW 2 major objections 5 minor 43 references
To Measure What Isn't There -- Visual Exploration of Missingness Structures Using Quality Metrics
T0 review · 2 major / 5 minor · reviewed 2026-08-07 · deepseek-v4-flash
Pith's one-line read Six quality metrics expose the hidden structure of missing data.
desk verdict Useful formalization of missingness metrics, but the conditional-missingness evaluation needs a sensitivity analysis before the case-study findings can be trusted. 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 load-bearing machinery is a set of six per-variable or per-pair scores, equations (1) through (6). $QAM$ is the fraction of missing entries in a variable. $QJM_{mag}$ is the fraction of items jointly missing in both variables; $QJM_{dir} = P(\vec d_j,\vec d_k) - E(\vec d_j,\vec d_k)$ is the signed deviation from the chance expectation $E = P(\vec d_j) P(\vec d_k)$; and $QJM_{abs}$ is the absolute value of that deviation, so high scores flag pairs whose co-missingness is unlikely to be accidental. The conditional metrics $QCM_{DiD}$ and $QCM_H$ compare, for each direction, the histogram of recorded values in $\vec d_k$ for items missing in $\vec d_j$ against the histogram for all recorded items, using the Shimazaki-Shinomoto rule to set bin counts, and normalize by the maximum possible difference or entropy. These scores make high dimensionality tractable: instead of inspecting all pairs of hundreds of variables, the analyst sorts, filters, and lays out variables by the scores and inspects the small set of outlier pairs.
What would settle it
Take a dataset whose missing values are generated completely at random per variable (MCAR), with high per-variable missing rates so that many pairs have large joint missingness. If $QCM_{DiD}$ and $QCM_H$ frequently exceed their upper thresholds for these purely random pairs, the metrics cannot separate random from structured conditional missingness; the paper's own Section 5.4 observation predicts exactly this behavior, so an explicit receiver-operating-characteristic curve over synthetic MCAR data would settle how much of the case-study signal is artifact.
Extended reading notes
Core claim
The paper's central claim is that structural missingness in large, high-dimensional data can be surfaced by six quality metrics defined over the three patterns of Amount Missing, Joint Missingness, and Conditional Missingness. $QAM$ gives each variable a score between 0 and 1 for the relative share of missing values. For each variable pair, $QJM_{mag}$ measures the observed share of jointly missing items, $QJM_{dir}$ measures the signed difference between observed and expected joint missingness, and $QJM_{abs}$ measures the absolute size of that deviation. For each directed pair, $QCM_{DiD}$ compares the distribution of recorded values for items that are missing in the other variable against the overall distribution, while $QCM_H$ compares their Shannon entropies. The paper demonstrates that mapping these values to variable ordering, subset selection, node size, edge width and colour, and histogram/glyph displays lets users spot clusters of attributes whose missingness is too structured to be random. In the ICICLE case study, the metrics expose blocks of missingness tied to study protocol, such as clinical measures not recorded for healthy controls and mutually exclusive activity-measurement sessions, and point to a testable hypothesis that declining health caused later dropouts.
Load-bearing premise
The load-bearing premise is that the two conditional-missingness metrics give dependable signals even when only a handful of items are missing in one variable but recorded in the other; the paper itself notes in Section 5.4 that with high joint missingness these scores are forced high and uses an ad-hoc filter to suppress that effect.
Editorial extensions
If this is right
- Ordering variables by $QAM$ immediately separates attributes whose missingness would make simple imputation unreliable from those that are nearly complete.
- Pairs with high $QJM_{abs}$ and clearly positive or negative $QJM_{dir}$ can be prioritized for data-collection debugging, since their co-missingness cannot be explained by per-variable missing rates alone.
- High $QCM$ values in a direction $\vec d_j \to \vec d_k$ give an evidence-based reason to impute $\vec d_j$ using recorded values in $\vec d_k$, or to withhold imputation and model the missingness explicitly.
- The same metrics can be applied to categorical variables by treating categories as histogram bins, extending the method beyond numerical sensor data.
- In longitudinal studies, trends in $QAM$ and $QJM_{abs}$ across time points can track worsening cohort health or protocol drift as the study ages.
Reading between the lines
- The deviation-from-chance framing of $QJM_{dir}$ could be reused for any pairwise co-absence problem, such as co-occurring sensor failures or mutually exclusive survey response patterns; the paper does not state this application.
- The known instability of $QCM_{DiD}$ and $QCM_H$ when the conditioning subset is tiny suggests a natural extension: report a minimum-support count or confidence interval alongside each conditional score, and calibrate thresholds per dataset rather than using fixed cutoffs.
- A null-model test that permutes missingness within each variable while preserving marginal missing rates could turn these metrics into formal significance tests of non-random missingness; that test is not in the paper.
- If applied at the item level rather than the variable level, the metrics could flag individual records whose missingness profile is anomalous, a direction the paper does not explore.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper defines six quality metrics for missingness patterns—QAM, QJM_mag, QJM_dir, QJM_abs, QCM_DiD, and QCM_H—and demonstrates their use in variable ordering, filtering, and network, parallel-coordinates, and MissiG visualizations. Section 3 gives the definitions, Section 4 presents synthetically generated datasets with controlled missingness structures, and Section 5 applies the metrics to the ICICLE walking-monitoring dataset, reporting structures that are traced to data-collection procedures. The paper also acknowledges in Section 5.4 that the conditional-missingness metrics are problematic when the conditioning subset is small. The central claim is that these metrics can guide visual exploration of structured missingness in large high-dimensional data.
Significance. The contribution is potentially valuable: quality metrics tailored to missingness structures are a genuine gap in the visualization literature, and the proposed metrics are clearly specified and correctly normalized, including the division by 2 in Eq. (5) and by log(bk) in Eq. (6). The visual encodings are sensible, and the ICICLE case study is a rich real-world exemplar. The supplemental materials with synthetic datasets are a useful asset. However, the validation is not yet strong enough to support the effectiveness claim: the synthetic experiments largely confirm quantities that were planted using the same definitions, and the conditional-missingness metrics lack uncertainty quantification or a null-model baseline.
major comments (2)
- [§4.1, Tables 1–2; §4.3–§4.4] The synthetic evaluation plants missingness using exactly the quantities the metrics measure: JM patterns are generated by setting P(dj,dk) relative to E(dj,dk), which is what QJM_dir and QJM_abs compute by definition, and CM patterns are generated by placing missing values in predetermined value ranges, which is what QCM_DiD and QCM_H detect. The agreement reported in Sections 4.3 and 4.4 therefore confirms internal consistency, not detection power. Without a null model (e.g., MCAR replicates) or a comparison to standard missingness tests, the experiments do not establish that the metrics can distinguish structured missingness from chance, which is the central claim of Section 3. Please add a randomized-baseline evaluation reporting detection rates, precision/recall, or an equivalent performance measure.
- [§5.4; Eqs. (5)–(6)] The CM metrics estimate a histogram and an entropy from the subset DRk∩DMj. When this subset is small, QCM_DiD is positively biased and QCM_H is inflated by the negative small-sample bias of sample entropy, so high values do not necessarily imply conditional missingness. Section 5.4 correctly acknowledges this for high joint missingness, but the proposed filter QJM_dir < 0.05 does not control the subset size: writing P(both) for P(DMj∩DMk), the conditioning subset has size P(DMj) − P(both), which under near-independence is approximately P(DMj)(1−P(DMk)) and can be tiny even when QJM_dir is near zero. The thresholds 0.05 and 0.9 are applied once, with no sensitivity analysis or null distribution, and the case-study conclusions about Height, BMI, and MoCA rest on the surviving edges. Please provide a sampling distribution or an explicit minimum-support criterion for Eqs. (5)–(6), and validate the filter on synthetic data with known small-S regimes.
minor comments (5)
- [§4.1] The dataset is described as containing 106 patients, but 64 cancer patients plus 52 healthy controls sums to 116; please correct this inconsistency.
- [Table 1] The last row reports '38.3.1%' where a valid percentage is intended; please fix this typographical error.
- [§4.1] The phrase 'aN aNstrings' appears throughout; it should read 'NaN strings'.
- [§5.4 and figure captions] There are several typographical slips, including 'furhtermore' and 'zoomed in in figure 14'; these should be cleaned up before publication.
- [§5.4] The text describes the filter QJM_dir < 0.05 as indicating low joint missingness, but QJM_dir is a signed deviation from expected joint missingness, not a magnitude; the wording should clarify that the filter is selecting a mix of negative and small positive deviations.
Circularity Check
No significant circularity: the paper defines explicit quality metrics and demonstrates them on synthetic and real data; no prediction or fitted parameter reduces to its own inputs.
full rationale
The paper's contribution is a set of explicit quality-metric definitions (Eqs. 1-6), not a derivation of a population quantity from a fitted model. QAM is the missingness proportion, QJM_mag the joint missingness proportion, QJM_dir/QJM_abs the signed and absolute deviations from the independence baseline E(dj,dk)=P(dj)P(dk), and QCM_DiD/QCM_H are total-variation and normalized-entropy differences between a marginal and a conditional histogram. These are transparent, closed-form functions of the data; no parameter is fitted to a subset and then renamed as a prediction. The synthetic experiments in Section 4.1 plant missingness patterns using the very quantities the metrics report, e.g. setting P(dj,dk) equal to, above, or below E(dj,dk) for QJM_dir, but this is a controlled sanity check with known ground truth, not a circular derivation: the paper does not claim to predict the planted patterns from the metrics; it displays the metrics on data whose structure is already known. The ICICLE case study provides an external, real-world demonstration, and Section 5.4 openly acknowledges that QCM_DiD and QCM_H become unstable when the conditioning subset DRk ∩ DMj is small, proposing an explicit filter rather than claiming the raw metrics are universally valid. That limitation is a robustness or statistical-inference concern, not circularity. Self-citations to [16] and [11] supply background definitions of missingness patterns and the MissiG glyph design, but the validity of Eqs. 1-6 does not rest on those citations: the equations are stated in full and are computable from the data alone. No uniqueness theorem, ansatz smuggled in via citation, or renaming of a known result is used to force the paper's conclusions. The case-study findings are explicitly speculative and exploratory, further reducing any sense of a derived prediction. Overall, the derivation chain, to the extent there is one, is self-contained and non-circular.
Assumptions & free parameters
free parameters (3)
- Edge filter thresholds for CM exploration =
QJM_dir < 0.05 and QCM_DiD > 0.9
- Attribute selection thresholds in case study =
top 9 and top 23 attributes by QAM or QJM_abs
- Synthetic missingness generation parameters =
missingness 0 to 50 percent for AM, 20 to 50 percent for JM, 10 to 33 percent for CM; CM strengths 30, 60, and 90…
assumptions (3)
- domain assumption The three pattern classes Amount Missing, Joint Missingness, and Conditional Missingness are the relevant structure taxonomy for missingness analysis.
- domain assumption Expected joint missingness under chance is the product of the two variables' marginal missingness probabilities, E(dj,dk) = P(dj)P(dk).
- domain assumption Comparing the distribution of dk for items missing in dj with the overall distribution of dk reveals conditional missingness.
Cite this review
Pith. "Pith review of To Measure What Isn't There -- Visual Exploration of Missingness Structures Using Quality Metrics." pith.science (2026). https://pith.science/paper/OAVZE5U5
@misc{pith2026250523447,
author = {Pith},
title = {Pith review of: To Measure What Isn't There -- Visual Exploration of Missingness Structures Using Quality Metrics},
year = {2026},
howpublished = {\url{https://pith.science/paper/OAVZE5U5}},
note = {Machine review of arXiv:2505.23447}
}
read the original abstract
This paper contributes a set of quality metrics for identification and visual analysis of structured missingness in high-dimensional data. Missing values in data are a frequent challenge in most data generating domains and may cause a range of analysis issues. Structural missingness in data may indicate issues in data collection and pre-processing, but may also highlight important data characteristics. While research into statistical methods for dealing with missing data are mainly focusing on replacing missing values with plausible estimated values, visualization has great potential to support a more in-depth understanding of missingness structures in data. Nonetheless, while the interest in missing data visualization has increased in the last decade, it is still a relatively overlooked research topic with a comparably small number of publications, few of which address scalability issues. Efficient visual analysis approaches are needed to enable exploration of missingness structures in large and high-dimensional data, and to support informed decision-making in context of potential data quality issues. This paper suggests a set of quality metrics for identification of patterns of interest for understanding of structural missingness in data. These quality metrics can be used as guidance in visual analysis, as demonstrated through a use case exploring structural missingness in data from a real-life walking monitoring study. All supplemental materials for this paper are available at https://doi.org/10.25405/data.ncl.c.7741829.
Figures
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Reference graph
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doi: 10.1212/WNL.0000000000000066 13
Reviewed August 7, 2026 · model on record in the stance chip above.
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