Overview :

The usefulness of a test is often judged in how well it makes the diagnosis for the presence or absence of a disease.

A person with the disease who has a "positive" test is termed a true positive, whereas a person with the disease but a "negative" test result is termed a false negative.

A person without disease who has a "positive" result is termed a false positive, while a person without disease having a "negative" result is termed a true negative.

In real life things are not always clearcut; the distinction between positive and negative in a test result is sometimes artificial while it is not always possible to say if a person does or does not have a disease.

Braunwald E, Isselbacher KJ, et al (editors). Harrison's Principles of Internal Medicine, 11th edition. McGraw-Hill Book Publishers. 1987. page 7

Goldman L. Chapter 10: Quantitative aspects of clinical reasoning. pages 43-48. IN: Isselbacher KJ, Braunwald E, et al. Harrison's Principles of Internal Medicine, Thirteenth Edition. McGraw-Hill. 1994.

Panzer RJ, Black ER, Griner PF. Interpretation of diagnostic tests and strategies for their use in quantitative decision making. pages 17-28. IN: Panzer RJ, Black ER, et al. Diagnostic Strategies for Common Medical Problems. American College of Physicians. 1991.

Speicher C, Smith JW Jr.. Choosing Effective Laboratory Tests. WB Saunders. 1983. pages 50-51, and 210

>>>39.01.01 Incidence Rate

Overview:

The incidence rate is the number of new cases of a disease in the total population per unit time.

incidence rate =

= ((A) / (a + b + c + d)) / T)

where:

• A = number of new cases of a disease for given time period, which is a subset of all the true positives (a + c) ;

• (a + b + c + d) = sum of (true positives, false positives, false negatives, true negatives) = total population

• T = unit of time

References:

Goldman L. Chapter 10: Quantitative aspects of clinical reasoning. pages 43-48. IN: Isselbacher KJ, Braunwald E, et al. Harrison's Principles of Internal Medicine, Thirteenth Edition. McGraw-Hill. 1994.

Speicher C, Smith JW Jr.. Choosing Effective Laboratory Tests. WB Saunders. 1983., page 51