Positive predictive value

Positive predictive value is like predicting something will happen and then seeing if it really does happen.

For example, let's say you and your friend are playing outside, and you predict that it will rain today. You decide to check the weather forecast to see if your prediction is likely to happen. If the weather forecast says there is a high chance of rain (let's say 80%), then your positive predictive value is 80%. This means that out of 100 times you predicted rain, it will actually rain 80 times.

Now, let's say you predict it will snow tomorrow. You check the weather forecast and it says there is only a 20% chance of snow. Your positive predictive value is now 20%, meaning that out of 100 times you predict snow, it will only snow 20 times.

Positive predictive value is used a lot in medical tests. For example, if you take a pregnancy test and it comes back positive, the positive predictive value would be the likelihood that you are actually pregnant. If the positive predictive value is high, then it's a strong indication that you are pregnant.