Statistical analysis
’, handedness, pain
REGRESSION
First, descriptive statistics were calculated for age and body mass index (BMI), as well as the distribution of sex, education, job situation, and handedness. This was followed by analyses of the differences between the groups (electrical and thermal), calculated using the Student’s Then, the variables of interest were checked for outliers and prepared before the conduct of further statistical analyses: the pain ratings for each color and the baseline were aggregated into means. After, the first and the second pain baseline blocks were compared through the repeated-measures ANOVA, with ‘modality’ (electrical, thermal) as the between-subjects factor and ‘baseline’ (first, second) as the within-subjects factor. The baselines did not differ significantly, therefore they were combined into one. The baseline pain ratings were subtracted from the pain color ratings. Similarly, within both pain expectation blocks, the expectation baseline rating was subtracted from the expectation rating of every other color. Therefore, data analyses for pain and expectation were performed on the differences between the baseline (black) and the other colors.In the primary analyses on pain intensity, a two-way, mixed-design ANOVA was used with ‘modality’ (electrical, thermal) as the between-subjects factor and ‘color’ (differences between the baseline and each of the following: blue, green, grey, orange, pink, red, white, and yellow) as the within-subjects factor. Three additional ANOVAs of the same structure were conducted with respective additional factors: ‘Q1’ (yes, no), ‘Q2’ (yes, no), or ‘Q3’ (yes, no), in order to verify whether awareness of the study aim (Q1) and beliefs about the influence of colors on pain (Q2 and Q3) influenced the results.Also, a three-way, mixed-design ANOVA was performed on participants’ NRS expectation ratings. The ‘modality’ (electrical, thermal) was the between-subjects factor, while ‘color’ (differences between the black and each of the following: blue, green, grey, orange, pink, red, white and yellow) and ‘block ‘(first expectation block, second expectation block) served as the within-subject factors.The post-hoc tests were performed for the pain and expectation ratings to explore between-colors differences. Correlation and regression analyses were performed to explore the relationship between pain expectation related to colors at the beginning of the experiment and further pain intensity ratings.The alpha level was set at 0.05 for rejection of the null hypothesis. The Bonferroni correction was implemented for all analyses. The analyses were conducted using the IBM SPSS Statistics environment, version 26.0 (IBM Corp. 2019).