A multivariate analysis of variance revealed significant group differences in pre-to-post changes on measures of VHI , maximum phonation time , and cepstral peak prominence ( CPP ) in connected speech and vowels ( P = 0.003 , 0.013 , 0.025 , and 0.017 respectively ) , with a significant reduction of VHI ( Cohen 's d = 1.6 ) , increase in maximum phonation time ( Cohen 's d = 1.2 ) , increase of CPP in connected speech ( Cohen 's d = 1.2 ) , and increase of CPP in vowels ( Cohen 's d = 1.1 ) in the experimental group compared to the control group .