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Blinding Compliance Rate Calculator

Work out blinding compliance rate instantly with clear inputs, formula shown and shareable results.

About Blinding Compliance Rate Calculator

Blinding is tested by asking participants to guess their allocation. In a two-arm trial chance is 50%, so 58 correct guesses out of 100 gives a blinding index of 0.16 - some unblinding, worth flagging. An index near zero means guesses are no better than chance, which is what successful blinding looks like.

Formulas

Blinding index

index = (correct guess rate - chance rate) / (1 - chance rate)

Chance rate

chance = 1 / number of arms

Worked example

With the default values below, Blinding Compliance Rate Calculator returns Blinding Index of 0.1600. Change any input above and every figure here is recalculated in your browser.

Inputs used

Participants correctly guessing their allocationminimum 0
58
Participants who guessedminimum 1
100
Treatment armsminimum 2
2

Results

Blinding Index
0.1600
Correct Guess Rate
58.00%
Rate Expected By Chance
50.00%
Blinding Assessment
Some unblinding - interpret with caution

Step by step

  1. 1Values used
  2. 2Blinding index
  3. 3Chance rate
  4. 4Blinding Index= 0.1600
  5. 5Correct Guess Rate= 58.00
  6. 6Rate Expected By Chance= 50.00
  7. 7Blinding Assessment= Some unblinding - interpret with caution

Assumptions and limits

  • The result is derived only from the 3 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 4 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why do participants guess correctly?

Side effects are the main clue, along with symptom improvement. Active drugs with distinctive effects are notoriously hard to blind.

Should blinding be tested routinely?

CONSORT encourages reporting it. A broken blind does not invalidate a trial but must be considered when interpreting subjective outcomes.

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