Frequency trees

Task goals

• Read a frequency tree and identify what the grand total, a first-stage branch, and a second-stage (leaf) branch each represent.
• Find a missing frequency on a frequency tree by subtracting the known branch(es) from the relevant stage total.
• Convert a frequency to a probability or proportion by dividing by the grand total (an unconditional probability) or by a single branch's total (a conditional proportion, e.g. "of those who...").
• Compare proportions across two different branches of the same tree to judge which group is more/less likely to have a given outcome.
• Explain the difference between a frequency tree (counts at the nodes) and a probability tree (probabilities along the branches, summing to 1 at each split).