Sample size
SECONDARY
The sample size was calculated using a dedicated statistical software package (IBM SPSS Statistics 22.0; IBM Analytics, Armonk, NY, USA). The primary outcome (patient’s compliance behavior) was not used for sample size calculation due to the lack of data about this topic. One of the secondary outcomes was color change: considering a 2.4 standard deviation from a pilot study and the minimum difference to be detected from 3.3, with a 95% confidence level and a maximum acceptable error of 5%, each group required 20 participants. Considering a possible loss of patients, 10% of the total sample was added. The final calculation was 66 participants, once it is a parallel design trial.