Speech quality is postulated to consist of several perceptual attributes. Psychoacoustic experiments for Mandarin monosyllables were designed and conducted to investigate the relations between five abstract attributes, including intelligibility, clarity, naturalness, continuity and noise intrusiveness, and perceived integral speech quality. Experimental results demonstrate a good speech quality estimate can be obtained using a simple multivariate linear regression method. The linear regression analysis shows clarity has the most impact on speech quality, while intelligibility contributes little in the subjective assessment. These findings could be used to develop categorical-rating based objective speech quality measures in the future.