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 = @ , @ , @ , and @ respectively ) , with a significant reduction of VHI ( Cohen 's d = @ ) , increase in maximum phonation time ( Cohen 's d = @ ) , increase of CPP in connected speech ( Cohen 's d = @ ) , and increase of CPP in vowels ( Cohen 's d = @ ) in the experimental group compared to the control group .