For urn A, you will always be given the exact percentage of red marbles. For urn B, you will receive advice from someone who wants to help you who has estimated the percentage of red marbles in urn B. There are two sources, a friend and an expert:
The friend has no training in estimating percentages, but is trying to help you by giving you an estimate of the percentage of Red in Urn B.
The expert has been trained in estimating percentages by eye. The expert also makes an estimate of Urn B by eye.
These people are both trying to help you, but they do not know the exact percentages; they make their estimates by shaking the jar, looking through the clear glass, and estimating the percentage by eye.
Look at the first trial below, W1. In this case, we know that urn A has exactly 30 red marbles and 70 white ones. The friend, however, thinks that there are 70% red in urn B. If you think there are more than 30% red in the urn B, you should choose urn B. By choosing A, you know that you have exactly 30 out of 100 chances to win. But if the friend is right, there are more than twice as many red marbles in urn B. Some people will choose A and others will choose B.
If you strongly prefer A, click
far to the left, and if you strongly prefer B, click far to the right.
To indicate intermediate degrees of preference, click along the row of buttons closer to the
urn from which you would prefer to choose a marble.