Page 439 - Libro 2

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Quality Assurance Statistics
Terrence D. Case
OBJECTIVES
KEY TERMS
accuracy | gold standard | negative predictive value | positive predictive value | sensitivity | specificity
GLOSSARY
accuracy the overall percentage of correct results
gold standard a well-established and reliable testing parameter, which for vascular disease, is often angiography
Ultrasound is technology that is safe and reliable when used by well-trained sonographers in a de- partment that is focused on quality assurance (QA). QA refers to a program for the systematic monitor- ing and evaluation of the various aspects of vascular testing to ensure that standards of quality are being met. However, it has taken years of research and de- velopment to convince physicians and other health care providers that ultrasound technology alone is accurate in the assessment of vascular disease. To achieve that confidence, the ultrasound profession relied on statistics to demonstrate the effectiveness of sonography and Doppler in the assessment of vas- cular disease.
STATISTICS
Statistics is the science of making effective use of numerical data relating to groups of individu- als or experiments. It deals with all aspects of the collection, analysis, and interpretation of such data. In addition, statistics is used in the planning of the collection of data in terms of the design of surveys and experiments. This chapter will briefly review some of the common terminology and systems used
sensitivity the ability of a test to detect disease specificity the ability of a test to correctly identify
a normal result
to determine the accuracy of vascular ultrasound re- ports or studies.
COMPARING DIAGNOSTIC TESTS
The “Gold Standard”
Medical science has borrowed the term “gold stan- dard” to compare one form of a newer diagnostic test with another that is well-established and reli- able. The “gold standard” in vascular imaging typi- cally refers to the angiogram (or in some cases, a venogram). The angiogram has a long history of accuracy and, therefore, all newer types of vascu- lar imaging must be compared to it to determine the presence or absence of disease and the extent to which it presents. However, there are some risks with angiography, which may be as minimal as a hematoma at the insertion site to allergic reaction to the dye, which could end with either a stroke or even death. In medicine, the benefits must always outweigh the risks, and although ultrasound is considered safe and accurate now, it had to be first compared with the gold standard in order to estab- lish accuracy. Ideally, a vascular ultrasound would match the gold standard 100% of the time, but this is often not the case. There are various common
Define the term “gold standard”
Describe the common statistical terms including sensitivity, specificity, and accuracy
Define other commonly used statistical parameters
Calculate basic statistical values using a chi-square test
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