Standard scores

Standard scores allow you to compare values created from different scales to a common scale that is based on standard deviation units (1). Standard scores such as the T-score and z-score are used extensively, but not exclusively, in bone densitometry.

For example, imagine that a group of physicians, group A, was tested on their knowledge of bone densitometry. Arbitrarily, the highest score that could be made on the test was 75 and the lowest score that could be made was 25. A second group of physicians, group B, was also tested on their knowledge of bone densitometry. On this test, however, the highest score that could be made was 100 and the lowest score that could be made was 50. Sometime later, a physician from group A confided to a physician from group B that his score on the test was 70 and that he thought this score was generally above average for the test. The physician from group B, whose score was 75, was initially relieved to learn that he had outperformed his colleague on the test. Unfortunately, the physician from group B failed to recognize that two very different scales were used to grade the tests making it impossible to directly compare the raw scores of 70 and 75. The only way to compare how well the two physicians actually did, is to convert their test scores to a third, common scale. This can be done using any one of several standard score scales. Figure 3-1 illustrates the relationships among several standard score scales, including the T-score, z-score, and Army General Classification Test (AGCT) scale. Each of these scales assigns an arbitrary value on the scale to the raw average value. For each SD change from the raw average value, the standard score increases or decreases by a predetermined amount.

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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