The Vitamin A activity of beta-carotene compared to that of retinol is?

Beta-Carotene (provitamin A): This is found in plant foods. lt is cleaved in the intestine to produce two moles of  retinal. ln humans, this conversion is inefficient, hence beta-carotene possesses about  one-sixth vitamin A activity compared to that of retinol. Reference: Satyanarayana- Biochemistry, 3rd edition, pg-119