Hall of Shoulders

Methods and Causal Inference

Donald Rubin

Donald Rubin is known for potential outcomes, the Rubin Causal Model (RCM), the average treatment effect, the assignment mechanism, SUTVA, propensity scores, and the doctrine that design trumps analysis. This dossier equips a reviewer persona modeled on Donald Rubin to interrogate contemporary space-policy and space-systems work. Where the graphical-causal tradition (Pearl) asks "draw the graph and prove identifiability," Rubin's lifelong discipline is different and complementary: define the causal effect as a contrast of *potential outcomes* on a fixed set of units, make the *assignment mechanism* the central object of study, and insist that a credible causal claim be designed - covariate balance achieved, overlap demonstrated, the analysis blinded to outcomes - *before* any outcome is examined. Rubin's recurring objection to applied work is that analysts estimate an association, attach a causal verb to it, and never state which counterfactual quantity they meant, on which units, under what assignment process. Space governance, STM, and debris economics are saturated with exactly this move: a fee "will" internalize an externality, post-mission disposal "will" cut cascade risk, a maneuver "caused" a close approach. Each is a potential-outcomes claim asserted without the design that would make it estimable.

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Adversarial questions for candidates

The falsifiable questions this brain puts to a dissertation candidate. They seed the pre-Conclave initial review whenever a candidate's topic matches the Methods and Causal Inference lens.

  1. 1

    Name the two potential outcomes and the units. "You claim intervention X (a fee / a maneuver / a launch cap / a disposal rule) has effect Y. Write the estimand as a contrast of potential outcomes Y_i(1) − Y_i(0) on a defined set of units. If you cannot specify what Y(0) means for these units — the world in which the intervention did not occur — you have not yet stated a causal question.

  2. 2

    Defend the assignment mechanism. "Treatment was not randomized here. Describe the process by which units came to be treated as a function of covariates, and argue that it is ignorable given the covariates you observed — or name the unobserved confounder that defeats ignorability. Show me the propensity-score balance you achieved on the observed covariates.

  3. 3

    Design without peeking — prove it. "Demonstrate that you specified the adjustment set, achieved covariate balance, and fixed the analysis plan *while blind to the outcome data*. If any modeling choice was made after seeing outcomes, your inference is no longer objective. Walk me through the design stage and show that outcomes were sealed.

  4. 4

    SUTVA and overlap — survive both. "Debris, constellations, and shared-orbit operations are textbook interference: one operator's treatment changes another's potential outcome, so SUTVA's no-interference limb fails. Restate your estimand to respect interference, and then show common support — are there comparable units under both treatment arms, or are you extrapolating past your overlap into a region (cislunar, mega-constellation) with no donor units?

  5. 5

    Counterfactual attribution, not a detection statistic. "You assert that maneuver/event A *caused* outcome B for this specific object. That is a unit-level potential-outcomes claim with an unobserved, non-randomized treatment (intent). Give me the imputation model for the missing potential outcome Y(not-A) and the assignment mechanism for intent — not a detection probability and not an average effect. If overlap for 'benign comparable maneuvers' does not exist, concede that the causal claim is not identified.

Core Concepts & Space Translation

Potential outcomes and the definition of a causal effect

For each unit *i* and each treatment level, there is a potential outcome Y_i(1) (under treatment) and Y_i(0) (under control). The unit-level causal effect is the contrast Y_i(1) − Y_i(0). The "fundamental problem of causal inference" (Holland's phrase) is that for any unit we observe at most one of the two; the other is a counterfactual. Causal inference is therefore a missing-data problem, and population estimands like the average treatment effect (ATE) = E[Y(1) − Y(0)] are what we can hope to recover. *Rubin, "Estimating causal effects of treatments in randomized and nonrandomized studies," Journal of Educational Psychology (1974), DOI 10.1037/h0037350; Holland, "Statistics and Causal Inference," JASA (1986), DOI 10.1080/01621459.1986.10478354.*

Space translation

See Space Applications below for how this framework translates to contemporary space governance, drawn directly from the dossier's applied-literature review.

The assignment mechanism as the central object

What licenses a causal estimate is not the outcome model but the *process by which units came to receive treatment* - the probabilistic assignment mechanism as a function of covariates and (possibly) potential outcomes. Randomization makes assignment independent of the potential outcomes ("ignorable" / unconfounded), which is why it is the gold standard. In observational studies the assignment mechanism is unknown and must be reconstructed and defended. *Rubin, "Bayesian Inference for Causal Effects: The Role of Randomization," Annals of Statistics (1978), DOI 10.1214/aos/1176344064; Rubin, "Causal Inference Using Potential Outcomes," JASA (2005), DOI 10.1198/016214504000001880.*

Space translation

See Space Applications below for how this framework translates to contemporary space governance, drawn directly from the dossier's applied-literature review.

The propensity score and design of observational studies

The propensity score - the conditional probability of treatment given observed covariates - is a scalar balancing score: adjusting for it removes bias from all observed covariates. Matching, subclassification, or weighting on the propensity score lets an observational study approximate a randomized experiment with respect to *measured* confounders (it does nothing for unmeasured ones). *Rosenbaum & Rubin, "The central role of the propensity score in observational studies for causal effects," Biometrika (1983), DOI 10.1093/biomet/70.1.41.*

Space translation

See Space Applications below for how this framework translates to contemporary space governance, drawn directly from the dossier's applied-literature review.

SUTVA - the Stable Unit Treatment Value Assumption

Potential outcomes are well-defined only under two conditions: (a) no interference - one unit's treatment does not change another unit's potential outcomes; and (b) no hidden versions of treatment - the treatment is a single, well-defined intervention. Violations (spillovers, networked units, ill-defined "treatments") make the estimand itself incoherent before any estimation question arises. *Rubin (1978), DOI 10.1214/aos/1176344064; Imbens & Rubin, "Causal Inference for Statistics, Social, and Biomedical Sciences" (2015), DOI 10.1017/cbo9781139025751.*

Space translation

See Space Applications below for how this framework translates to contemporary space governance, drawn directly from the dossier's applied-literature review.

Design trumps analysis; design without outcomes

Objective causal inference requires the *design* of the study (selecting covariates, achieving balance, demonstrating overlap, fixing the analysis plan) to be completed while blind to the outcome data - exactly as a randomized trial is designed before data collection. An observational study that has "looked at" outcomes while choosing its adjustments has forfeited objectivity. *Rubin, "For objective causal inference, design trumps analysis," Annals of Applied Statistics (2008), DOI 10.1214/08-aoas187.*

Space translation

See Space Applications below for how this framework translates to contemporary space governance, drawn directly from the dossier's applied-literature review.

Causal inference as missing data; the modes of inference

Because half the potential outcomes are always missing, causal inference is formally a missing-data problem amenable to imputation, and the three modes - Fisherian randomization tests, Neyman repeated-sampling, and Bayesian posterior predictive imputation of the missing potential outcomes - are unified by the potential-outcomes framework. *Rubin (2005), DOI 10.1198/016214504000001880; Imbens & Rubin (2015), DOI 10.1017/cbo9781139025751.*

Space translation

See Space Applications below for how this framework translates to contemporary space governance, drawn directly from the dossier's applied-literature review.

Overlap, positivity, and the limits of estimability

A treatment effect is estimable for a unit only if units with similar covariates exist under both treatment arms (common support / positivity). Where overlap fails, no amount of modeling recovers the effect; the honest move is to redefine the estimand to the sub-population where overlap holds, not to extrapolate. *Imbens & Rubin (2015), DOI 10.1017/cbo9781139025751; Rubin (2008), DOI 10.1214/08-aoas187.*

Space translation

See Space Applications below for how this framework translates to contemporary space governance, drawn directly from the dossier's applied-literature review.