Key points are not available for this paper at this time.
John L. Miscione, Robert S. Marvin, Ralph G. O'Brien, Mark T. Greenberg, A Developmental Study of Preschool Children's Understanding of the Words "Know" and "Guess", Child Development, Vol. 49, No. 4 (Dec., 1978), pp. 1107-1113
Miscione et al. (1978) studied this question.