Impairment
As a secondary outcome measure, allergy-related impairment in quality of
life was assessed using the short form of the
Rhinitis/Rhinoconjunctivitis Quality of Life Questionnaire. This is the
German translation of the Mini Rhinoconjuctivitis Quality of Life
Questionnaire (MiniRQLQ) 29. Through 14 items, the
MiniRQLQ assesses the degree of impairment caused by allergy-related
symptoms. Two items refer to practical problems (e.g., ”having to rub
nose or eyes”) and three items each refer to limitations in activities
(e.g., ”sleep [difficulty sleeping through the night and/or falling
asleep at night]”), nasal symptoms, eye symptoms and other complaints
(e.g., ”irritability”). Respondents indicate the degree of impairment
for each item on a seven-point Likert scale (0 = “not at all” to 6 =
“extremely”). The instruction was slightly adapted so that the items
referred to the last 14 days, instead of the last 7 days, to ensure
comparability with the primary endpoint. The MiniRQLQ is a reliable and
valid questionnaire that is sensitive to symptom changes29,30. Cronbach’s alpha was α = .90 at T1, α = .91 at
T2 and α = .90 at T3.
Medication
Use
To assess whether participants took any medication against their
allergic symptoms, they were asked to choose one of three options: 1)
“I regularly take medication against my allergic symptoms”; 2) “I
take medication against my allergic symptoms on demand”; 3) “I don’t
take any medication against my allergic symptoms”.
Additional
questionnaires
In addition, we also assessed participants’ expectations and hopes
regarding the placebo treatment, the extent to which they felt informed
about placebos, their actual knowledge about placebos, their
self-efficacy beliefs, and their beliefs about a potential relationship
between their allergic symptoms and COVID-19 (see supplement).
Statistical Analyses
After data screening, we performed an intention-to-treat analysis by
estimating the missing values of the two persons who dropped out using
the expectation maximization procedure according to methodological
recommendations 31,32. For the main analysis, we
conducted two separate analyses of covariance (ANCOVA), with the
severity and frequency of allergic symptoms at T2 as the dependent
variable (DV), treatment (OLP vs. TAU) as a between-subjects factor, and
baseline allergic symptoms (T1) as a covariate. For the secondary
endpoint, we performed another ANCOVA with T2 impairment as the DV and
T1 impairment as a covariate. Subsequently, we added medication use (no
medication vs. regular medication vs. medication on demand) as an
additional between-subjects factor to the aforementioned ANCOVAs. Type-1
error levels were set at 5%. All analyses were conducted using IBM SPSS
Statistics Version 27.