## What is a positive prediction?

The likelihood that an individual with a positive test result truly has the particular gene and/or disease in question. Also called PPV.

**What is positive predictive power in psychology?**

Definition. Positive predictive value (PPV) represents the probability that a person has a disease or condition given a positive test result. That is, it is the proportion of individuals with positive test results who are correctly identified or diagnosed.

### What are positive and negative predictive values?

Positive predictive value is the probability that subjects with a positive screening test truly have the disease. Negative predictive value is the probability that subjects with a negative screening test truly don’t have the disease.

**What is a good PPV and NPV?**

Positive predictive value (PPV) and negative predictive value (NPV) are directly related to prevalence and allow you to clinically say how likely it is a patient has a specific disease.

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Negative predictive value (NPV)

Prevalence | PPV | NPV |
---|---|---|

20% | 69% | 97% |

50% | 90% | 90% |

## Why is PPV important?

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.

**Why is positive predictive value important?**

Positive predictive value:

It is the ratio of patients truly diagnosed as positive to all those who had positive test results (including healthy subjects who were incorrectly diagnosed as patient). This characteristic can predict how likely it is for someone to truly be patient, in case of a positive test result.

### What is a good PPV value?

A PPV of 99% indicates that with a positive assay result there’s a 99% chance of it being correct. Likewise, with a 49% PPV, there is only a 49% chance that the patient is actually positive. Depending on the intended use of the product, one, both, or neither of these predictive values might be sufficient.

**What is considered a high PPV?**

A PPV of 99% indicates that with a positive assay result there’s a 99% chance of it being correct. Likewise, with a 49% PPV, there is only a 49% chance that the patient is actually positive.

## What does a low PPV mean?

When the prevalence of preclinical disease is low, the positive predictive value will also be low, even using a test with high sensitivity and specificity. For such rare diseases, a large proportion of those with positive screening tests will inevitably be found not to have the disease upon further diagnostic testing.

**What does high PPV mean?**

A high PPV indicates that a positive biomarker test result is likely correct. Similarly, a NPV estimates the proportion of subjects with a negative test result based on FNs and TNs that are correctly diagnosed. NPV is defined as the ratio of TN / (TN + FN) and is reported as a percentage.