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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