Is the New World translation of Hebrews 11:1 adequate?

Hebrews 11:1 is one of the most important definitions of faith given in the NT. Is this translation of the NWT adequate or does it add points that are not to be found in the Greek original:

Faith is the assured expectation of what is hoped for, the evident demonstration (footnote: Or "convincing evidence") of realities that are not seen.

Here is the Greek:

Westcott and Hort / [NA27 variants] Ἔστιν δὲ πίστις ἐλπιζομένων ὑπόστασις, πραγμάτων ἔλεγχος οὐ βλεπομένων·

Specifically, is "evident demonstration" (or "convincing evidence") an acceptable translation of ἔλεγχος? Other translations have "conviction" (e.g., ESV, NASB).

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