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Table 1 Frequencies of nine different blinding scenarios by PIL categories

From: Does different information disclosure on placebo control affect blinding and trial outcomes? A case study of participant information leaflets of randomized placebo-controlled trials of acupuncture

Scenario

Experimental Group

Control Group

Possible Interpretation [10]

FD % (n)

DD/MI % (n)

S1

Random guess

Random guess

Possibly most ideal from the scientific or statistical perspective

11.8 (2)

18.2 (2)

S2

Random guess

Opposite guess

Rare

5.9 (1)

9.1 (1)

S3

Random guess

Unblinded

Possibly little treatment effect and no effect in control group

5.9 (1)

0 (0)

S4

Unblinded

Unblinded

Possibly problematic

11.8 (2)

9.1 (1)a

S5

Unblinded

Opposite guess

Ideal – patients tend to have wishful thinking, strong placebo effect, and any treatment administered is perceived as real treatment

29.4 (5)

45.5 (5)

S6

Unblinded

Random guess

Possibly problematic – patients in control group do not know what to expect in the absence of treatment

29.4 (5)

18.2 (2)

S7

Opposite guess

Opposite guess

Rare

0 (0)

0 (0)

S8

Opposite guess

Random guess

Rare

5.9 (1)

0 (0)

S9

Opposite guess

Unblinded

No treatment effect at all or patients may have low expectations

0 (0)

0 (0)

  1. There were 17 and 11 studies in FD, and DD/MI category, respectively. aAmong the 11 studies in DD/MI category, only one article belonged to MI category
  2. Here, the term “Unblinded” generally means “More correct guess,” not broken blinding literally
  3. Random guess: −0.2 < BI < 0.2; unblinded: BI ≥ 0.2; opposite guess: BI ≤ −0.2 [10]
  4. BI Blinding index, DD Deceptive disclosure of placebo acupuncture, FD Full disclosure of placebo acupuncture, MI Missing information on placebo acupuncture, PIL participant information leaflet