Definition of population
 Revised: 2001-10-28

Question: What is your definition of the target population? Please use the sore throat as a model although the idea may be applied to other diagnoses as well.

In the diagnostic situation we are dealing with several different populations:

Definitions of populations:
Definition --- Example from the strep throat ---
  1. The entire population

The entire population
  1. All individuals that during a period experience symptoms possibly indicating presence of the disease we are looking for.
 All individuals that during a year experience a sore throat
  1. All individuals attending the health care system because of these symptoms
 All individuals attending the health care system due to a sore throat
  1. All individuals attending the health care system with this symptom suitable for testing
 All individuals attending the health care system due to a sore throat and lacking obvious signs of a viral etiology.
  1. All individuals attending the health care system with this symptom suitable for testing and with a positive test
 All individuals attending the health care system due to a sore throat and lacking obvious signs of a viral cause having a positive test (rapid test or throat culture)
  1. All individuals attending the health care system with this symptom suitable for testing and with a negative test
 All individuals attending the health care system due to a sore throat and lacking obvious signs of a viral cause having a negative test (rapid test or throat culture)

The population A and B are not seen by the health care system. Some of the individuals attending health care (population C) are not suitable for testing.

Definition of populations used in EPV

Etiologic predictive value (EPV) focus on the population attending health care and having clinical signs making them suitable for testing (population D). Population E is used to calculate post-test probability for disease in case of a positive test, P(D+|T+) and population F is used to calculate post-test probability for absence of disease in case of a negative test, P(D-|T-).

Other WebPages of interest

Other pages with subjects that might be of interest is:

(You can click on these links to quickly see the pages)

References

  1. Evans CE, McFarlane AH, Norman GR, Neale KA, Streiner DL. Sore throats in adults: Who sees a doctor? Can Fam Physician 1982;28:453-8.
     
  2. Hoffmann S. Incidence and management of sore throat in general practice. Scand J Prim Health Care 1986;4:143-50.
     
  3. Meland E, Digranes A, Skjaerven R. Assessment of clinical features predicting streptococcal pharyngitis. Scand J Infect Dis 1993;25:177-83.
     
  4. Hoffmann S. An algorithm for a selective use of throat swabs in the diagnosis of group A streptococcal pharyngo-tonsillitis in general practice. Scand J Prim Health Care 1992;10:295-300.
     
  5. Gunnarsson RK. When shall the doctor take the test. Dissertation: Microbiologic diagnostic tests when asymptomatic carriers are present. Aspects of the use of conventional throat and nasopharyngeal cultures as examples. Göteborg: Department of primary health care and department of medical microbiology, Göteborg University, Sweden; 2001, pp 65-7.

Ronny Gunnarsson MD PhD
Department of Primary Health Care
Göteborg University
SWEDEN

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