During the 3 min after the histamine skin prick (but before physician assurance), itchiness increased similarly for both conditions (
Badj,T = 11.85 units/min vs.
Badj,C = 11.55 units/min;
ΔB = − 0.30,
z = − 0.22,
p = .83, 95% CI − 2.96 to 2.37,
d = − 0.05). After the physician assurance, itchiness declined significantly faster in the assurance condition (
Badj,T = − 2.51 units/min vs.
Badj,C = − 1.26 units/min;
ΔB = − 1.24,
z = − 1.96,
p = .05, 95% CI − 2.49 to 0,
d = 0.39) (Fig.
1). Consequently, participants who received assurance felt significantly less itchy immediately after the physician encounter at 9 min post-skin prick (0.48 standard deviations lower) than control participants (
Madj,T = 20.20 vs.
Madj,C = 28.70;
B = − 8.50,
z = − 2.34,
p = .019, 95% CI − 15.62 to − 1.38,
d = − 0.48). After minute 9, itchiness declined in both conditions by a similar amount (
Badj,T = − 2.01 units/min vs.
Badj,C = − 1.39 units/min vs;
ΔB = 0.62,
z = −1.43,
p = .154, 95% CI − 0.23 to 1.47,
d = 0.31), such that the condition difference was also present at minute 12 (
Madj,T = 16.03 vs.
Madj,C = 22.67;
B = −6.64,
z = −1.99,
p = .047, 95% CI − 13.19 to −0.08,
d = − 0.37) but subsided by minute 15 (
Madj,T = 11.86 vs.
Madj,C = 16.64;
B = −4.78,
z = −1.35,
p = 0.178, 95% CI − 11.73 to 2.17) (Fig.
1). That assurance had an immediate effect that weakened over time is unsurprising given the reaction was expected to decline over time in both conditions.
6