Predictive value of tests is the
probability
Probability is the branch of mathematics concerning numerical descriptions of how likely an Event (probability theory), event is to occur, or how likely it is that a proposition is true. The probability of an event is a number between 0 and ...
of a target condition given by the result of a test,
often in regard to
medical test
A medical test is a medical procedure performed to detect, diagnose, or monitor diseases, disease processes, susceptibility, or to determine a course of treatment. Medical tests such as, physical and visual exams, diagnostic imaging, geneti ...
s.
*In cases where
binary classification
Binary classification is the task of classifying the elements of a set into two groups (each called ''class'') on the basis of a classification rule. Typical binary classification problems include:
* Medical testing to determine if a patient ha ...
can be applied to the test results, such yes versus no, test target (such as a substance, symptom or sign) being present versus absent, or either a
positive or negative test
Positive is a property of positivity and may refer to:
Mathematics and science
* Positive formula, a logical formula not containing negation
* Positive number, a number that is greater than 0
* Plus sign, the sign "+" used to indicate a posi ...
), then each of the two outcomes has a separate predictive value. For example, for positive or negative test, the predictive values are termed
positive predictive value
The positive and negative predictive values (PPV and NPV respectively) are the proportions of positive and negative results in statistics and diagnostic tests that are true positive and true negative results, respectively. The PPV and NPV de ...
or
negative predictive value
The positive and negative predictive values (PPV and NPV respectively) are the proportions of positive and negative results in statistics and diagnostic tests that are true positive and true negative results, respectively. The PPV and NPV de ...
, respectively.
*In cases where the test result is of a continuous value, the predictive value generally changes continuously along with the value. For example, for a
pregnancy test
A pregnancy test is used to determine whether a female is pregnant or not. The two primary methods are testing for the female pregnancy hormone (human chorionic gonadotropin (hCG)) in blood or urine using a pregnancy test kit, and scanning with u ...
that displays the urine concentration of
hCG, the predictive value increases with increasing hCG value.
A
conversion of continuous values into binary values can be performed, such as designating a pregnancy test as "positive" above a certain
cutoff value
In medicine and health-related fields, a reference range or reference interval is the range or the interval of values that is deemed normal for a physiological measurement in healthy persons (for example, the amount of creatinine in the blood ...
, but this confers a loss of information and generally results in less accurate predictive values.
See also
*
Positive predictive value
The positive and negative predictive values (PPV and NPV respectively) are the proportions of positive and negative results in statistics and diagnostic tests that are true positive and true negative results, respectively. The PPV and NPV de ...
*
Negative predictive value
The positive and negative predictive values (PPV and NPV respectively) are the proportions of positive and negative results in statistics and diagnostic tests that are true positive and true negative results, respectively. The PPV and NPV de ...
References
Medical tests
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