Purpose - The purpose of the paper is to compare measures of subjective and objective knowledge as well as usage/experience measures in a credence service environment for two different samples, namely college students and non-student adults. Design/methodology/approach - Data were collected from two independent samples using self-administered questionnaires and were analyzed using correlation and reliability analyses, factor analysis, discriminant analysis and one-way ANOVA. Findings - For the student sample, the results show that even though measures of subjective product knowledge, objective product knowledge, and product usage are correlated with one another, each represents one unique dimension of total product knowledge. The results for the non-student sample show that subjective and objective knowledge converge into one dimension, product usage is a second dimension, and vicarious product knowledge a third dimension. Research limitations/implications - One limitation of the present study is that its results are anchored in the context of hospitals and might thus be most relevant to this particular choice of service. In terms of implications, the "vicarious" component of total product knowledge the study uncovers for non-students is a promising field for future studies because it is identified as one of the dimensions of total knowledge for those non-student consumers who have a fairly low degree of objective knowledge and direct product experience. Practical implications - Marketing managers should to take into account that, for adults, subjective knowledge is a better indicator of their objective knowledge than for students (or perhaps similar segments). Originality/value - The present study is one of the first studies to investigate simultaneously the three dimensions of consumer product knowledge in a credence service environment