For the first branch, refer to the table to obtain the following:

The total number of people in the experiment was N = 800+600+400+200 = 2,000.
Of those, the number using the cream was 800+400 = 1,200.
Therefore, the probability that a randomly chosen subject used the cream was 1,200/2,000 = 3/5.

Since the sum of the probabilities on the branches leaving a node is 1, the other branch must be labeled 2/5, giving the following first stage:

Starting at the "C"-node, we are looking at a total of 800+400 = 1,200 people who used the cream (see the chart), of whom 800 improved. This gives a probability of 800/1,200 = 2/3, and hence leads to part of the next stage:

Starting at the "P"-node, we are looking at a total of 600+200 = 800 people who used the placebo (see the chart), of whom 600 improved. This gives a probability of 600/800 = 3/4, and hence leads to the completed tree:

Just close this window to return to the tutorial.