Navigation Links
Positive predictive value


The positive predictive value, or precision rate, is the proportion of patients with positive test results who are correctly diagnosed. It is considered the physician's gold standard, as it reflects the probability that a positive test reflects the underlying condition being tested for.

Contents

Worked example

Relationships among terms
Condition
(as determined by "Gold standard")
True False
Test
outcome
Positive True Positive False Positive
(Type I error, P-value)
Positive predictive value
Negative False Negative
(Type II error)
True Negative Negative predictive value

Sensitivity

Specificity
A worked example
the Fecal occult blood (FOB) screen test is used in 203 people to look for bowel cancer:
Patients with bowel cancer
(as confirmed on endoscopy)
True False ?
FOB
test
Positive TP = 2 FP = 18 = TP / (TP + FP)
= 2 / (2 + 18)
= 2 / 20 ≡ 10%
Negative FN = 1 TN = 182 = TN / (TN + FN)
182 / (1 + 182)
= 182 / 183 ≡ 99.5%

= TP / (TP + FN)
= 2 / (2 + 1)
= 2 / 3 ≡ 66.67%

= TN / (FP + TN)
= 182 / (18 + 182)
= 182 / 200 ≡ 91%

Related calculations

  • False positive rate (α) = FP / (FP + TN) = 18 / (18 + 182) = 9% = 1 - specificity
  • False negative rate (β) = FN / (TP + FN) = 1 / (2 + 1) = 33% = 1 - sensitivity
  • Power = 1 − β

Definition

The Positive Predictive Value can be defined as

or, alternatively,

Where prevalence is the probability that the disease exists in the population. The positive predictive value is also known as the statistical power in statistics and probability of detection, PD , in engineering.

Problems with positive predictive value

Predictive values are often used in medical research to evaluate the usefulness of a diagnostic test. Hence the PPV is used to indicate the probability that in case of a positive test, that the patient really has the specified disease. However there may be more than one cause for a disease and any single potential cause may not always result in the overt disease seen in a patient.

An example is the microbiological throat swab used in patients with a sore throat. Usually publications stating PPV of a throat swab are reporting on the probability that this bacteria is present in the throat, rather than that the patient is ill from the bacteria found. If presence of this bacteria always resulted in a sore throat, then the PPV would be very useful. However the bacteria may colonise individuals in a harmless way and never result in infection or disease. Sore throats occurring in these individuals is caused by other agents such as a virus. In this situation the gold standard used in the evaluation study represents only the presence of a bacteria (that might be harmless) but not a causal bacterial sore throat illness. It can be proven that this problem will affect positive predictive value far more than negative predictive value. To evaluate diagnostic tests where the gold standard looks only at potential causes of disease, one may use an extension of the predictive value termed the Etiologic Predictive Value.

See also

References

  • Altman DG, Bland JM (9 Jul 1994). "Diagnostic Tests 2 - Predictive Values". British Medical Journal 309 (6947): 102.
  • Gunnarsson RK, Lanke J. The predictive value of microbiologic diagnostic tests if asymptomatic carriers are present. Statist. Med. 2002; 21:1773-1785

'"/>


(Date:8/20/2014)... 20, 2014 The National Association ... $1.24 million Science Education Partnership Award (SEPA) grant ... NAHN’s collaborative project with the Hispanic Communications Network ... , This collaborative NIH R25 program has been ... linguistic diversity among health professionals by recruiting and ...
(Date:8/20/2014)... City, New Jersey (PRWEB) August 20, 2014 ... in meeting the needs of an estimated tens of ... introduction of the new Bill A3525—a bill that would ... patients to grow their own cannabis—earlier this summer by ... horticultural training for medicinal quality marijuana is growing. , ...
(Date:8/20/2014)... 20, 2014 Verndale is pleased to ... list; an exclusive list ranking the fastest-growing private companies ... according to their yearly percentage revenue growth over a ... on the Inc. 5000 list where it ranked number ... offers its clients a wide range of digital marketing ...
(Date:8/20/2014)... B. E. Smith, the only full-service leadership solutions ... to lead a national chief operating officer ... Ore. The top executive search firm in ... more than 900 healthcare executives into organizations. , ... healthcare organization serving a population of more than 35,000 ...
(Date:8/20/2014)... Biosimilars, which are similar versions ... an abbreviated process, could reap billions in health ... Services, Inc.’s (AIS) Specialty Pharmacy News offers coverage ... Food and Drug Administration’s (FDA) recent acceptance of ... , Drugmaker Sandoz said July 24 that the ...
Breaking Medicine News(10 mins):Health News:National Association of Hispanic Nurses (NAHN) Receives Five-Year Federal Grant from the National Institutes of Health (NIH) 2Health News:National Association of Hispanic Nurses (NAHN) Receives Five-Year Federal Grant from the National Institutes of Health (NIH) 3Health News:Oaksterdam University to Host Four-Day Educational Marijuana Horticultural Seminar Aug 23-26; Training Fills Information Gap for Medical Marijuana Caregivers and Patients 2Health News:Oaksterdam University to Host Four-Day Educational Marijuana Horticultural Seminar Aug 23-26; Training Fills Information Gap for Medical Marijuana Caregivers and Patients 3Health News:For the 8th Time, Verndale Has Been Honored on the Inc. 5000 List 2Health News:Good Shepherd Health Care System Retains B. E. Smith to Recruit New COO 2Health News:Good Shepherd Health Care System Retains B. E. Smith to Recruit New COO 3Health News:AIS Newsletter Tracks Latest Developments in Biosimilars Market as FDA Accepts First Application 2Health News:AIS Newsletter Tracks Latest Developments in Biosimilars Market as FDA Accepts First Application 3
... a scheme that would provide safe drinking water to the ... day after the Bollywood star Aamir Khan offered his support ... Gaur told IANS that a Rs.17-crore (Rs.10.7 million) scheme has ... in the 13 gas-hit localities of Bhopal was contaminated. ...
... is a breather for those who suffer from severe ... revealed that breathing a special gas mixture may help ... Patients revealed that after breathing the gas, their endurance ... breath. These findings have been published in the American ...
... revolution of sorts. A clue into what might be ... at reducing// or totally obliterating the side-effects by evolving ... information. Indeed this will be a whole new story ... M. Issa, a pharmacologist and clinical epidemiologist is the ...
... what extent their perception influences our behavior has often intrigued ... Current Directions in Psychological Science reveals that that we are ... in which their feelings are expressed towards us. This is ... thought process. ,Infact, these perceptions often linger in the ...
... antiviral coating on bank notes, vending machines and photocopiers ... ,Materials researcher Guagang Ren at Queen Mary ... metal, metal oxide and ceramic nanoparticles that have strong ... ,Applying the coatings to buttons on ...
... issue of Current Directions in Psychological Science finds that other ... The article explains that we are tied to each other. ... feelings can be a contagious, strong influence. ,Explaining ... the influences of other people that affect us without our ...
Cached Medicine News:Health News:State Govt To Provide Safe Drinking Water To Bhopal Gas Victims 2Health News:COPD Patients portray improved exercise performance after breathing a Special Gas 2
Other medicine definitionOther Tags