2.6. Statistical Analysis
dermatochalasis
PTOSIS, DERMATOCHALASIS
Twenty-seven patients were needed per treatment group to detect a difference of 8.3 in the HIT-6 score between groups A and B at 6 and 12 months, with a two-sided 5% significance level and a power of 85%, allowing for a 15% attrition rate and 10% for possible non-parametric testing (G* Power version 3.1.9.6, University of Kiel, Germany). The mean HIT-6 score is based on pre-and postoperative differences between two groups, i.e., the blepharoplasty and ptosis surgery groups [The data were analysed using IBM SPSS Statistics version 26.0 (IBM Corp., Armonk, NY, USA). The Shapiro–Wilk test, Kolmogorov–Smirnov test, and graphical interpretation of Q–Q plots were used to determine the distribution of the data. All the tests were carried out for both sides of the patients’ faces (left and right) and were included in the data set. The independent samples t-test, Chi Square test, and Fisher’s exact test were applied where appropriate to test baseline differences between the groups.Pre- and post-blepharoplasty differences in eyebrow height and HIT-6 score within groups were analysed using the Friedman test followed by pairwise comparisons, and Bonferroni adjusted Differences between groups A and B regarding eyebrow height in millimetres, baseline eyebrow height, gender, age, dermatochalasis severity score, and amount of removed tissue during surgery were also evaluated using GEE. The residuals showed a Gaussian distribution and the model with the lowest information criterion was used (i.e., m-dependent for the a and b landmarks, exchangeable correlation structure for landmark c).The differences in eyebrow height change between the landmarks were also evaluated using the Friedman test with pairwise comparisons and by applying Bonferroni adjusted To assess inter-observer agreement in measuring patients’ eyebrow height, all the measurements were performed by two raters (M.H.J.H. and M.C.) and intraclass correlation coefficient (ICC, two-way mixed effects model, single measurement, absolute agreement) was calculated. All the patients’ eyebrow height measurements were repeated to provide an intraclass correlation coefficient (ICC, two-way mixed effects model, single measurement, absolute agreement). The ICC values were interpreted as follows: 0.00–0.20, poor; 0.20–0.40, fair; 0.40–0.60, moderate; 0,60–0.80, good; 0.80–1.00, excellent [The Friedman test was used to compare the post-surgical RMS, median frequencies, and the index (RMS/maximal amplitude) with the preoperative EMGs within each treatment group. Subsequently, a post-hoc test was carried out and Bonferroni adjusted The differences between groups A and B were evaluated using GEE. The GEE model included the EMG values, baseline sEMG values, gender, age, dermatochalasis severity score, and the amount of tissue removed during surgery. The residuals showed a Gaussian distribution, and the model with the lowest information criterion was used (i.e., exchangeable correlation structure). Only the RMS and median frequency values were transformed (log10) to achieve a Gaussian distribution of the residuals.The correlation between the pre- and postoperative change in EMG values (mean frontalis muscle RMS of right and left eye), eyebrow height (mean height at the b and ‘b landmarks), and HIT-6 score was analysed with the Spearman correlation coefficient. The correlation coefficients, r values, were interpreted as follows: between 0–0.19, very weak; 0.2–0.39, weak; 0.40–0.59, moderate; 0.6–0.79, strong; and 0.8–1, very strong [In addition, the baseline variables were correlated with changes in any other variable during the follow-up.The baseline variables were EMG values (mean frontalis muscle RMS of right and left eye), eyebrow height (mean height at the b and ‘b landmarks), or HIT-6 score. The pre-and both the 6- and 12-month postoperative changes in these variables were used. This was done in order to investigate if baseline values could ‘predict’ the change in outcomes.