Effects of Laughter Yoga on Symptom Severity, Hope, and Life Engagement in Patients Undergoing Chemotherapy; A Randomized Controlled Study

The sample size was determined through an a priori power analysis using G*Power software (version 3.1.2). The test family was "t tests" and the statistical test was "Means: Difference between two independent means (two groups)". Based on Cohen's standard effect size references it was determined that a total of 52 participants (26 per group) would be sufficient to achieve 80% power with a large effect size (two-tailed, Cohen's d = 0.80, α = 0.05). The choice of a large effect size was justified by recent evidence from laughter interventions in cancer. To account for a potential 15% attrition rate, 8 additional participants were included, resulting in a total sample size of 60 individuals. Following the completion of the study, the effect sizes for each variable were reported in their respective tables. Inclusion criteria: (1) age ≥18, (2) pathologically confirmed cancer diagnosis, (3) be able to communicate, and (4) voluntary participation. Exclusion criteria: (1) diagnosed psychiatric disorders that may interfere with study participation or communication, (2) receiving medical treatments other than chemotherapy, (3) significant hearing or vision loss, (4) prior experience with laughter therapy, or (5) an unstable clinical condition. Discontinuation Criteria: (1) withdrawal request, (2) worsening of clinical condition, (3) change in treatment protocol.

A list of eligible patients was provided by the unit charge nurse. Of the 87 assessed, 24 patients did not meet inclusion criteria and 3 patients declined participation. Due to the nature of the laughter yoga intervention, participants and the first author (who performed the sessions) could not be blinded. After obtaining voluntary consent, eligible patients were randomized into intervention (n=30) and control (n=30) groups with a 1:1 allocation ratio using a computer-generated random number list (randomizer.org). To ensure allocation concealment, randomization was managed by an independent researcher who did not recruit patients or perform the sessions. Once a patient was enrolled, the independent researcher provided the group assignment to the first researcher. This centralized approach prevented the first researcher from knowing the sequence in advance, thereby reducing potential selection bias. Immediately following randomization, but prior to the collection of pre-test and the commencement of the intervention, five patients (3 from the intervention group and 2 from the control group) were excluded due to unforeseen changes in their medical treatment protocols. Since these individuals left the study before any baseline or post-test assessments could be conducted, their data were unavailable for inclusion. Consequently, a per-protocol analysis was performed with the remaining 55 patients (27 intervention, 28 control) who completed the trial. To minimize bias, data analysis was conducted by an independent statistician who remained blinded to the group assignments throughout the study.

Explanation regarding protocol improvements: Initial registration reflected the study plan at the time of registration. Before enrollment of the first participant, certain methodological and operational details were further refined based on the clinical setting, characteristics of the appropriate patient population, discussions with the clinical team, and a review of the relevant literature. These refinements included a more detailed definition of the intervention duration, the randomization procedure, and the eligibility criteria. Final procedures were determined prior to the enrollment of the first participant on January 30, 2025, and were consistently applied throughout the study.