Two assessments of mental imagery vividness were compared through meta-analysis, the Vividness of Visual Imagery Questionnaire (VVIQ), and trial-by-trial ratings of vividness. Each vividness assessment was further divided into behavioural/cognitive or neuroscientific measures. It was found that the average effect size magnitude for trial-by-trial vividness exceeded that of the VVIQ for behavioural/cognitive, but not neuroscientific measures. However, the average effect sizes magnitude for neuroscientific measures was generally greater than behavioural/cognitive ones. Additionally, the average effect sizes magnitude for trial-by-trial vividness ratings was generally greater than the VVIQ. It is suggested that trial-by-trial ratings, in conjunction with neuroscientific measurement, may provide a more precise and reliable measure of mental imagery vividness. Despite face validity, unique observations correlating trial-by-trial vividness ratings with the VVIQ were weak to moderate on average. Theoretical considerations on the empirical validity of the construct of vividness are discussed.