4 groups of 18 Ss each went through 3 decks of 100 cards, each card contained 1 of 2 letters. The 3 100-card sequences were randomly drawn with a probability of .67 for 1 of the letters and .33 for the other. Prediction proportions on the last 30 cards of each deck approximated .67 for groups which predicted the letters on each card only, and was significantly higher for groups which predicted and also estimated the letter proportions for the deck. Deviations from theoretical values discussed in terms of the effects of estimates upon predictions. Availability of information had no effect upon predictions or estimates. (PsycINFO Database Record (c) 2006 APA, all rights reserved)