# Positive Predictive Value (PPV)

A Positive Predictive value wil give you an indication of the chance that your symptom matches the result. This often is displayed as a PPV percentage.
Experience shows us that the percentages can be used as:

• 70-100% = Reliable
• 30-70% = Moderately reliable
• 0-30% = Not reliable

#### How to increase?

To increase reliability you can:
• Complete the symptom with more details eg (Belly pain after eating)
• Specify a 2nd symptom via "Add Symptom"

Note!
This value is related with your inserted symptoms. So this value can be different for "Cough" or "Dry cough". This behavior is inherent tot the mechanism that is used within this symptom checker.

#### How is it calculated?

PVW [%] = a / (a+b) * 100
a = Sortingvalue specific selection
b = Sum of sortingvalues of other related diseases in relation to your inserted symptom.

Calculation example: For calculating the PVW for the symptom "Headache" in the syndrome "Migraine":
a = "Headache -> Migraine" with a sortingvalue/weight factor of 10
b = Sum of the other relationships:
- "Headache -> Tired eyes" has a sortingvalue/weightfactor of 4