Reproducible figures, tables and data provenance
Preserve the numerical and procedural information needed to reconstruct a physical result, including units, normalization and correlations.
On this page
The question for today
What you’ll understand
- Connect plotted densities to counts, efficiencies and exposure.
- Propagate covariance through normalization and unit changes.
- Describe a reproducible record without equating reproducibility with correctness.
A figure communicates a physical conclusion, but its pixels rarely contain enough information to reproduce the inference. Bin edges, normalization, covariance, calibration and analysis versions all affect what the points mean. Reproducible reporting preserves the path from observations to derived quantities and the assumptions made along that path. This final lesson treats a two-bin hypothetical cross-section measurement and a unit conversion. The calculations show how apparently cosmetic presentation decisions can change numerical meaning when their metadata or covariance transformations are lost.
State exactly what every plotted number represents
A bin count, an efficiency-corrected yield, an integrated cross section and a differential cross section are distinct quantities. Divide a selected count by efficiency and integrated luminosity to estimate the bin's integrated cross section under a simple no-migration model. Divide once more by bin width to obtain an average density within that bin. Unequal widths make the distinction visible: a taller count bar need not imply a proportionally taller density. A plotted bin center also requires a convention; it does not replace the stored edges.
Record whether values are before or after background subtraction, acceptance correction and unfolding. A detector response can mix truth bins, so separate binwise efficiency corrections are not a universal unfolding method. Store statistical and systematic components with enough information to preserve their correlations, along with the ordering of entries. A list of total error bars cannot reconstruct a likelihood for arbitrary theory comparisons. If asymmetric uncertainties are reported, explain whether they are interval endpoints, likelihood changes or another convention.
Transform covariance with the values
For a linear conversion z equals A times y, covariance transforms with A on the left and its transpose on the right. Unit conversion therefore squares the numerical scale factor for variances and applies both factors to each covariance. The same rule propagates bin densities into an integrated cross section using bin widths as weights. Forgetting the off-diagonal terms can incorrectly make a common normalization uncertainty shrink when bins are added. Rounding should be delayed until after these operations.
For nonlinear transformations, a Jacobian gives a first-order approximation whose adequacy depends on uncertainty size and curvature. Exact distribution propagation or simulation may be needed near boundaries or for strongly asymmetric ratios. Retain enough numerical precision in machine-readable tables to reproduce the displayed result and avoid covariance matrices made non-positive by coarse rounding. Label whether an uncertainty is a standard deviation, a confidence interval or posterior content, and give the level and construction for intervals.
Preserve a checkable chain of evidence
A useful analysis record links raw or accessible derived inputs to calibration versions, event-selection rules, transformations, fitted models and final numerical artifacts. It includes the source version, relevant configuration, software environment and random seeds when stochastic computations are used. Seeds alone do not guarantee identical execution across changed algorithms or numerical libraries. A content hash can identify the exact input bytes but cannot establish their physical correctness, provenance or permission for use without associated metadata.
Store tables in a documented machine-readable form and link them to figures, descriptions, units and immutable versions. HEPData provides a physics example of structured tables, auxiliary resources and versioned identifiers; its data-release practices illustrate why a citation should identify a particular record version. Independent reproduction should compare physical quantities and tolerances, not merely rerun one plotting command. An exactly reproduced mistake remains a mistake, so residual checks, calibration validation and independent arithmetic belong beside the provenance record rather than being replaced by it.
Work it through
Two bins with a common luminosity uncertainty
Use counts 10 and 20, efficiencies 0.5 and 0.25, bin widths 1 and 2 GeV, and integrated luminosity . Assume independent Poisson counts, no background or migration, and a shared 10% luminosity uncertainty treated to first order. Find the density estimates and total covariance.
The denominators luminosity times efficiency times width are both numerically five in reciprocal-pb times GeV. The density estimates are therefore 2 and , while the integrated bin cross sections are two and eight pb.
The plug-in statistical variances of the densities are and in squared density units. Their statistical covariance is zero under the independent-count assumption.
The shared normalization adds , giving diagonal additions 0.04 and 0.16 and off-diagonal entries 0.08. The total covariance has rows (0.44, 0.08) and (0.08, 0.96), in squared density units.
The density vector is (2, 4) pb GeV⁻¹ and its covariance rows are (0.44, 0.08) and (0.08, 0.96) in pb² GeV⁻².
The living notebook
Explore the model
Interactive lab · function
Area and height are distinct reported quantities
Reset and set BOTH Coefficient a = 1 and Position x = 1; predict y = 1 and signed area 1/3. For a fresh comparison, Reset and set a = 1 and x = 2; predict y = 4 and signed area 8/3.
- y at chosen x
- 0.608
- Tangent slope · 2ax
- 1.35
- Signed area · ax³/3
- 0.182
This lab uses only y = ax². Playback traces the curve within the fixed integration interval from 0 to x; it does not estimate numerical error or change the chosen point. Parameter changes pause playback and recompute the model at the current elapsed time. Reset restores both parameters and returns time to zero. Playback starts paused. Adjust either parameter, then choose Play or Step.
Look forThe instrument integrates the fixed quadratic ax² from zero to x. It illustrates that endpoint height and integrated value differ; it does not bin data, normalize cross sections, unfold detector response or preserve data provenance.
Pause & reason
Check your understanding
Your turn
Try it yourself
An archived length vector is (1,2) m with covariance rows (0.04,0.01) and (0.01,0.09) in square meters. Convert the vector and covariance to centimeters, then compute the variance of the difference of the two lengths.
Take a moment to make a prediction or work it out on paper. Open a hint when you need one.
Give me a hint
Apply the same factor 100 to each length and one factor for each index of covariance.
Compare with the solution
The vector becomes (100,200) cm. Multiplying every covariance entry by 10,000 gives rows (400,100) and (100,900) in square centimeters. The difference is minus one hundred cm and its variance is . The standard deviation is about 33.2 cm. Omitting the off-diagonal term would give thirteen hundred instead, and retaining the old numerical covariance after changing units would be a much larger inconsistency.
Keep the idea
Take it with you
- Figures need definitions, units, bin edges and uncertainty conventions.
- Covariance must follow normalization, integration and unit transformations.
- Versioned inputs and analysis records support reproduction but do not prove correctness.
Read further
Original sources and deeper explanations to follow at your own pace.
Optional progress, saved in this browser when available. Revisit any lesson at any time.
Lesson not marked complete.