Читать книгу Medical Statistics - David Machin - Страница 79

Many studies involve a comparison of two groups. We may wish to combine simple summary measures to give a summary measure that in some way shows how the groups differ. Given two proportions one can either subtract one from the other, or divide one by the other.

Suppose the results of a clinical trial, with a binary categorical outcome (positive or negative), to compare two treatments (a new test treatment versus a control) are summarised in a two by two contingency table as in Table 3.3. The results of this trial can be summarised in a number of way sas in Table 3.3 below.

Table 3.3 Example of two by two contingency table with a binary outcome and two groups of subjects.

	Treatment group
Outcome	Test	Control
Positive	a	b
Negative	c	d
Total	a + c	b + d