Blind analysis and researcher degrees of freedom

Suppose several candidate analyses would each produce a calibrated local p-value under a background-only model. Reporting only the smallest one changes the statistic being interpreted. The probability of at least one small p-value is usually larger than the local threshold. For independent tests the complement probability factors; for correlated selections it generally does not. Neighboring mass windows, alternate cuts and related fit models often share the same events, so counting them as independent trials can be wrong in either direction.

An analysis protocol can define the family of searches and calibrate its global statistic by a model or simulation of that entire search. A Bonferroni threshold controls the family-wise error through the union bound without assuming independence, although it may be conservative. Data exploration is useful for developing physical models, but its inferential status should be visible. Treating a hypothesis suggested by a fluctuation as if it had been selected beforehand discards the selection step that created it.

A hidden signal region can prevent event-selection choices from responding to candidate signal events. Sidebands, simulation and independent control data can still support background and efficiency checks. For a precision measurement, a secret offset or sign transformation can hide the final parameter while preserving some relative comparisons. The scheme must be designed around what an analyst could infer indirectly from plots, fitted curves or correlated observables. A secret number that leaves the target visibly reconstructible provides little protection.

A common additive offset cancels from differences. That property can permit useful cross-checks while hiding an absolute mean, but it does not blind a measurement whose scientific target is that difference. Secret sign changes or transformed displays can be appropriate in other settings. Keep the transformation separate from the physics likelihood unless the likelihood transformation is explicitly part of a validated scheme. The unblinded result should be recovered by a documented reversible operation with the calibration and uncertainty conventions preserved.

Before revealing the protected result, record event selection, calibration choices, likelihood, interval construction, principal diagnostics and the conditions for unblinding. Reviewers should be able to judge the measurement chain using those diagnostics without requiring agreement with a preferred result. A genuine coding or detector problem found later can still require correction. Preserve its reason, timing and impact rather than forcing an incorrect analysis to remain frozen or silently optimizing it after seeing the answer.

A held-out sample can provide an additional check after exploratory development, provided it has remained independent of those choices and is analyzed under a fixed rule. Repeatedly inspecting that same holdout and adapting again consumes its protection. Blinding also cannot repair a wrong noise model, an omitted calibration correlation or undisclosed exclusions. A credible report distinguishes planned inference, exploratory findings, sensitivity analyses and post-unblinding corrections, allowing later readers to reconstruct the actual procedure and the scope of its claimed error probabilities.