positive predictive value

陽性的中率

WordNet

1. fix or determine the value of; assign a value to; "value the jewelry and art work in the estate"
2. the amount (of money or goods or services) that is considered to be a fair equivalent for something else; "he tried to estimate the value of the produce at normal prices" (同)economic value
3. (music) the relative duration of a musical note (同)time value, note value
4. relative darkness or lightness of a color; "I establish the colors and principal values by organizing the painting into three values--dark, medium...and light"-Joe Hing Lowe
5. the quality (positive or negative) that renders something desirable or valuable; "the Shakespearean Shylock is of dubious value in the modern world"
6. a numerical quantity measured or assigned or computed; "the value assigned was 16 milliseconds"
7. an ideal accepted by some individual or group; "he has old-fashioned values"
8. reckoned, situated or tending in the direction which naturally or arbitrarily is taken to indicate increase or progress or onward motion; "positive increase in graduating students"
9. a film showing a photographic image whose tones correspond to those of the original subject
10. the primary form of an adjective or adverb; denotes a quality without qualification, comparison, or relation to increase or diminution (同)positive degree
11. indicating existence or presence of a suspected condition or pathogen; "a positive pregnancy test" (同)confirming
12. having a positive charge; "protons are positive" (同)electropositive, positively charged
13. formally laid down or imposed; "positive laws" (同)prescribed
14. characterized by or displaying affirmation or acceptance or certainty etc.; "a positive attitude"; "the reviews were all positive"; "a positive benefit"; "a positive demand"
15. greater than zero; "positive numbers"
16. (usually used in combination) having value of a specified kind; "triple-valued"
17. held in great esteem for admirable qualities especially of an intrinsic nature; "a valued friend"; "precious memories" (同)precious
18. of or relating to prediction; having value for making predictions (同)prognostic, prognosticative
19. beliefs of a person or social group in which they have an emotional investment (either for or against something); "he has very conservatives values"

PrepTutorEJDIC

1. 〈U〉(…の)『価値』,値打ち,有用性,重要性《+of+名》 / 〈U〉〈C〉(…の)『価格』,値段《+of+名》 / 〈U〉〈C〉《米》《修飾語句を伴って》(払った金銭に対する)正当な値打ち / 〈C〉(単語の)意味,意義 / 〈C〉値,数値 / 〈C〉音の長短 / 〈C〉色価,(色の)明暗の度 / 〈C〉《複数形で》(道義・倫理などの)価値基準,価値観 / (ある金額に)…‘を'『評価する』,見積もる《+名+at+名〈金額〉》 / …‘を'『高く評価する』,尊重する,重んじる
2. 『肯定した,同意の』 / 『実際的な,』積極的な,建設的な / 《補語にのみ用いて》『確信のある』,自信のある / (事が)疑問の余地がない,明確な;(言葉が)はっきりした / 《名詞の前にのみ用いて》《話》全くの,文字どおりの / (生体の反応が)陽性の / (数が)正の,プラスの;(気電が)陽の;(写真で)陽画の / (形容詞・副詞の比較変化で)原級の / 明確(明白)なもの / (形容詞・副詞の)原級 / (写真の)陽画,ポジ / (数学で)正数
3. 貴重な,高く評価される,大切な

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/12/19 10:53:26」(JST)

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In statistics and diagnostic testing, the positive predictive value, or precision rate is the proportion of positive test results that are true positives (such as correct diagnoses). It is a critical measure of the performance of a diagnostic method, as it reflects the probability that a positive test reflects the underlying condition being tested for. Its value does however depend on the prevalence of the outcome of interest, which may be unknown for a particular target population. The PPV can be derived using Bayes' theorem.

Although sometimes used synonymously, a positive predictive value generally refers to what is established by control groups, while a post-test probability refers to a probability for an individual. Still, if the individual's pre-test probability of the target condition is the same as the prevalence in the control group used to establish the positive predictive value, the two are numerically equal.

Definition

The Positive Predictive Value is defined as

where a "true positive" is the event that the test makes a positive prediction, and the subject has a positive result under the gold standard, and a "false positive" is the event that the test makes a positive prediction, and the subject has a negative result under the gold standard.

The following diagram illustrates how the positive predictive value, negative predictive value, sensitivity, and specificity are related.

		Condition (as determined by "Gold standard")
		Condition Positive	Condition Negative
Test Outcome	Test Outcome Positive	True Positive	False Positive (Type I error)	Precision = Σ True Positive Σ Test Outcome Positive
	Test Outcome Negative	False Negative (Type II error)	True Negative	Negative predictive value = Σ True Negative Σ Test Outcome Negative
		Sensitivity = Σ True Positive Σ Condition Positive	Specificity = Σ True Negative Σ Condition Negative	Accuracy

Note that the positive and negative predictive values can only be estimated using data from a cross-sectional study or other population-based study in which valid prevalence estimates may be obtained. In contrast, the sensitivity and specificity can be estimated from case-control studies.

If the prevalence, sensitivity, and specificity are known, the positive predictive value can be obtained from the following identity:

Worked example

Suppose the fecal occult blood (FOB) screen test is used in 2030 people to look for bowel cancer:

		Patients with bowel cancer (as confirmed on endoscopy)
		Condition Positive	Condition Negative
Fecal Occult Blood Screen Test Outcome	Test Outcome Positive	True Positive (TP) = 20	False Positive (FP) = 180	Positive predictive value = TP / (TP + FP) = 20 / (20 + 180) = 10%
	Test Outcome Negative	False Negative (FN) = 10	True Negative (TN) = 1820	Negative predictive value = TN / (FN + TN) = 1820 / (10 + 1820) ≈ 99.5%
		Sensitivity = TP / (TP + FN) = 20 / (20 + 10) ≈ 67%	Specificity = TN / (FP + TN) = 1820 / (180 + 1820) = 91%

The small positive predictive value (PPV = 10%) indicates that many of the positive results from this testing procedure are false positives. Thus it will be necessary to follow up any positive result with a more reliable test to obtain a more accurate assessment as to whether cancer is present. Nevertheless, such a test may be useful if it is inexpensive and convenient. The strength of the FOB screen test is instead in its negative predictive value - which, if negative for an individual, gives us a high confidence that its negative result is true.

Problems with positive predictive value

Other individual factors

Note that the PPV is not intrinsic to the test—it depends also on the prevalence. Due to the large effect of prevalence upon predictive values, a standardized approach has been proposed, where the PPV is normalized to a prevalence of 50%. PPV is directly proportional to the prevalence of the disease or condition. In the above example, if the group of people tested had included a higher proportion of people with bowel cancer, then the PPV would probably come out higher and the NPV lower. If everybody in the group had bowel cancer, the PPV would be 100% and the NPV 0%.

To overcome this problem, NPV and PPV should only be used if the ratio of the number of patients in the disease group and the number of patients in the healthy control group used to establish the NPV and PPV is equivalent to the prevalence of the diseases in the studied population, or, in case two disease groups are compared, if the ratio of the number of patients in disease group 1 and the number of patients in disease group 2 is equivalent to the ratio of the prevalences of the two diseases studied. Otherwise, positive and negative likelihood ratios are more accurate than NPV and PPV, because likelihood ratios do not depend on prevalence.

When an individual being tested has a different pre-test probability of having a condition than the control groups used to establish the PPV and NPV, the PPV and NPV are generally distinguished from the positive and negative post-test probabilities, with the PPV and NPV referring to the ones established by the control groups, and the post-test probabilities referring to the ones for the tested individual (as estimated, for example, by likelihood ratios). Preferably, in such cases, a large group of equivalent individuals should be studied, in order to establish separate positive and negative predictive values for use of the test in such individuals.

Different target conditions

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. There is potential to mixup related target conditions of PPV and NPV, such as interpreting the PPV or NPV of a test as having a disease, when that PPV or NPV value actually refers only to a predisposition of having that disease.

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 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

• Binary classification
• Sensitivity and specificity
• Negative predictive value
• False discovery rate
• Relevance (information retrieval)
• Receiver-operator characteristic
• Gain (information retrieval)
• Diagnostic odds ratio

References and notes

UpToDate Contents

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• 1. 生物統計学および疫学に関する一般用語集 glossary of common biostatistical and epidemiological terms
• 2. 診断的検査の評価 evaluating diagnostic tests
• 3. 予防のためのエビデンスに基づいたアプローチ evidence based approach to prevention
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• Brentnall AR1, Vasiljević N, Scibior-Bentkowska D, Cadman L, Austin J, Szarewski A, Cuzick J, Lorincz AT.
• International journal of cancer. Journal international du cancer.Int J Cancer.2014 Sep 15;135(6):1425-32. doi: 10.1002/ijc.28790. Epub 2014 Mar 5.
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• Clinical endocrinology.Clin Endocrinol (Oxf).2014 Sep;81(3):432-9. doi: 10.1111/cen.12433. Epub 2014 Mar 13.
• OBJECTIVE: Follicular variant of papillary thyroid carcinoma (FVPTC) is a common variant of papillary thyroid carcinoma (PTC), but the association between BRAF mutation and the clinicopathological and ultrasonographical characteristics of FVPTC has not been well studied. The aim of this study was to
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• Doba Nobutaka,Tokuda Yasuharu,Goldstein Nathan E.,Kushiro Toshio,Hinohara Shigeaki,徳田 安春
• Experimental gerontology 47(8), 638-643, 2012-08
• … A score of 0 had a 93% negative predictive value for frailty while a score of 4 had a 70% positive predictive value. …
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• Positive and Negative Predictive Value

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Positive predictive value (PPV) The probability that a person with a positive test result has, or will get, the disease. Mentioned in: Genetic Testing predictive value a measure used by clinicians to interpret diagnostic test results. See ...

Related Pictures

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★リンクテーブル★

リンク元	「特異度」「感度」「陽性適中度」「陽性的中率」
関連記事	「value」「positive」「valued」「predictive」

「特異度」

　　[★]

英

specificity

関

感度、有病率(検査前確率)、陽性適中度 陽性予測値 positive predictive value、陰性適中度 陰性予測値 negative predictive value、感度と特異度

• 無病者における検査結果が陰性である確率(流れが分かる実践検査マニュアル上巻 p.35)

	疾患あり	疾患なし
検査陽性	a 真陽性	b 偽陽性
検査陰性	c 偽陰性	d 真偽性

Sp= d / ( b + d )

感度と特異度

• 公衆衛生学的な視点から有用
• 検査をすることによって集団の中からできるだけ疾病のある人を発見したい。

「感度」

　　[★]

英

sensitivity

同

敏感度

関

特異度、有病率(検査前確率)、検査後確率、陽性適中度　陽性的中率 positive predictive value、陰性適中度 陰性的中率 negative predictive value、感度と特異度、陽性尤度比

• 有病者における検査結果が陽性である確率(流れが分かる実践検査マニュアル上巻 p.35)

	疾患あり	疾患なし
検査陽性	a 真陽性	b 偽陽性
検査陰性	c 偽陰性	d 真偽性

Sn= a / ( a + c )

「陽性適中度」

　　[★]

英

predictive value of positive test, positive predictive value

同

陽性反応適中度 (SUB)

関

陰性適中度、感度、特異度

[show details]

陽性的中率 : 約 29,600 件
陽性的中度 : 約 951 件
陽性適中率 : 約 21,800 件
陽性適中度 : 89 件

陽性反応適中度 : 約 8,020 件
陽性反応的中度 : 約 5,830 件

• 「陽性予測率」とか訳されている場合があるが、これは一般的ではない感じ

陽性適中度と陰性適中度

• 臨床医学的視点から有用
• 検査をすることによって、その患者さんの疾病の有無を知りたい。

「陽性的中率」

　　[★]

英

positive predictive value

関

陽性適中度

• 検査が陽性の場合に疾患である確率

「value」

　　[★]

• n.

• 値、価値

• v.

• 評価する

関

account、appraisal、appraise、appreciate、appreciation、assess、assessment、characterization、estimate、estimation、evaluate、evaluation、judgement、judgment、worth

　 　 　 　 　 　 　 　

「positive」

　　[★]

• adj.

• 陽性の、正の、積極的な、ポジティブな

関

active、actively、aggressive、offensive、positively、positivity

　 　 　 　 　 　 　 　 　

「valued」

　　[★]

• adj.

• 価値ある

関

meritorious、valuable、worth、worthwhile、worthy

　 　 　

「predictive」

　　[★]

• adj.

• 予測的な

関

anticipatory、predictively