A total of 17 variables were evaluated: Independent variables were categorized as (1) age, (2) sex, (3) disease duration, (4) l-dopa equivalent dose (LED), (5) H & Y stage, (6) total UPDRS score, (7) UPDRS part III, (8) UPDRS part IV, (9) MMSE, (10) Zung depression score, (11) Zung anxiety score, (12) BFI, (13) SF-8, (14) sum score of items on PDSS (excluding items 6 and 7, associated with dream and hallucinations, respectively, which were rated from the direction of good to bad sleep), (15) dream-enactment behavior (absent = 0, present = 1), (16) nightmares (absent = 0, present = 1), and (17) increased doses of antiparkinsonian medications, such as dopamine agonists, trihexyphenidyl, amantadine, and zonisamide (absent = 0, present = 1). Variables that were significantly related to falling on univariate logistic regression analysis (P < 0.05) were entered into multivariate logistic regression analysis using forced entry. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated. Correlations of each variable were also evaluated by Spearman's rank-correlation test. To analyze the statistical significance of differences in these variables between groups, categories were evaluated by the Mann–Whitney U test, followed by Fisher's exact probability test (Fig. 1). SPSS software (Version 18; SPSS, Inc., Chicago, IL) was used for statistical analysis.