Type and site of melanoma

Use this page to show that the conditional probabilities are found by rescaling rows (or columns) of joint probabilities so each row (or column) has the same total (1.0). E.g.

Click the formulae for the conditional probabilities to do the stacking.

(The values are actually sample proportions rather than probabilities but the diagram illustrates the concept.)

The diagram is based on a real data set based on a study based on 400 who had been diagnosed with malignant melanoma. For each patient, the site of the tumour and its histological type were recoded.

  Site
Type of tumour Head & neck Trunk Extremities
Hutchinson's 22 2 10
Superficial spreading 16 54 115
Nodular 19 33 73
Indeterminate 11 17 28

The sample proportions are treated as joint probabilities in the diagram.