During the study, the international research team conducted a meta-analysis of 103 consumer knowledge research studies that took place between 1980 and 2007.
They compared objective knowledge (what people know) with subjective knowledge (what they think they know). They compared product knowledge to service or health-related knowledge, durable products to non-durable ones, and fun products to practical products.
They found higher correlations between objective and subjective knowledge with products than with non-products such as services and health-related information.
"Overall, our results suggest that people are not overly knowledgeable regarding how knowledgeable they are," said the researchers.
"They can deceive themselves into believing they are more knowledgeable than they are.
"Our results indicate that if a comparison is made relative to an expert, consumers' beliefs regarding their knowledge are more consistent with their actual knowledge than if a comparison had been made relative to an average person," they added.
The study appears in the Journal of Consumer Research.