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In the pharmaceutical industry, "breaking the blind" refers to the
process of revealing the name of the specific drug (or placebo, as the
case may be) that has been given to a participant in a double-blind
study or clinical trial.
http://answers.google.com/answers/threadview/id/515012.html

unblinded - The decision to stop the blinded or double-blinded process in a clinical trial and reveal the treatment assignment of an individual trial ...
www.acria.org/treatment/treatment_edu_fall03-win04update_te...
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治験分野の同義表現:　キーオープン、開鍵、開封、開票

In English
　As a noun:
　　code breaking
　　code opening
　　unblinding
　As a verb:
　　open the code
　　break the code
　　open the blind
　　open the blinding code
　　unblind
　　break the blinding

ただし下記のような文脈での"break the blind"などは「盲検性を台無しにしてしまう」と言うような意味になるので注意する必要がある:
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Obvious side effects in drug-treated subjects cue everyone about which treatment they are getting. This breaks the blind, making objective studies impossible.
http://criticalthinkrx.org/pdf/m3/Module-3-Complete-Slide-Pr...
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