Sensitivity and Specificity

Sensitivity and specificity are easily illustrated by considering a population of 1000 women in whom the spine bone density has been measured. A cut point can be chosen, most simply by picking a T-score such as -2.5 to determine the exact percentages of women with spine T-scores of -2.5 or poorer and spine T-scores better than -2.5. The women with T-scores of -2.5 or poorer are considered diseased. Based on World Health Organization (WHO) criteria,2 they have osteoporosis. The women with T-scores better than -2.5 are considered nondiseased in this example. They do not have osteoporosis, although many of them may be osteopenic. By using the T-score to pick a cut point that defines the categories of diseased and nondiseased, quantitative continuous bone density data has been converted into two qualitative nominal data categories.

In this example, illustrated in Table 3-3, there are 500 women in the diseased group and 500 women in the nondiseased group. All of the women are asked to complete a

2 See Chapter 9 for a discussion of the WHO criteria for the diagnosis of osteoporosis.

Table 3-3 The Results of a Diagnostic Test in 1000 Individuals with a Disease Prevalence of 50%

Table 3-3 The Results of a Diagnostic Test in 1000 Individuals with a Disease Prevalence of 50%

Essentials of Human Physiology

Essentials of Human Physiology

This ebook provides an introductory explanation of the workings of the human body, with an effort to draw connections between the body systems and explain their interdependencies. A framework for the book is homeostasis and how the body maintains balance within each system. This is intended as a first introduction to physiology for a college-level course.

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