The present investigation carried out acoustic analyses of vowels in clear and conversational speech produced by 41 talkers. Mixed-effects models were then deployed to examine relationships among acoustic and perceptual data for these vowels. Acoustic data include vowel duration, steady-state formant frequencies, and two measures of dynamic formant movement. Perceptual data consist of vowel intelligibility in noise for young normal-hearing and elderly hearing-impaired listeners, as reported by Ferguson in 2004 and 2012 [J. Acoust. Soc. Am. 116, 2365-2373 (2004); J. Speech Lang. Hear. Res. 55, 779-790 (2012)], respectively. Significant clear speech effects were observed for all acoustic metrics, although not all measures changed for all vowels and considerable talker variability was observed. Mixed-effects analyses revealed that the contribution of duration and steady-state formant information to vowel intelligibility differed for the two listener groups. This outcome is consistent with earlier research suggesting that hearing loss, and possibly aging, alters the way acoustic cues are used for identifying vowels.