Many medical experts study predictive value in medicine.
In the medical field, there can be a few a different outcomes from different medical tests: true positive (TP), true negative (TN), false positive (FP) and false negative (FN). Finding the predictive value is an equation that tells you percentage of times that the value, or end result, is a true value. You can use predictive value to determine both positive and negative true values. As long as you know values of the TP, TN, FP and/or FN, you can easily determine the predictive value.
Instructions
Positive Predictive Value
1. Know your equation. The equation for positive predictive value is:
TP / TP + FP x 100 = percent of predictive value of a positive result
2. Add the value of your variables. For this example, let's say that the number of true positives (TP) is 103, and the number of false positives (FP) is 67.
103 / (103 + 67 ) x 100 = ?
3. Add the TP and the FP together:
103 / 170 x 100 = ?
4. Divide 103 and 170:
0.60588 x 100 = ?
5. Multiply 0.60588 by 100 to find the result.
0.60588 x 100 = 60.588 or 60.6 percent predictive value of a positive result.
Negative Predictive Value
6. Know the equation. The equation for negative predictive value is:
TN / FN + TN x 100 = the percent of predictive value negative results
7. Add the value of your variables. For this example, let's say that the number of true negatives (TN) is 347, and the number of false negatives (FN) is 112:
347 / 112 + 347 x 100 = ?
8. Add the FN and the TN together:
347 / 459 x 100 = ?
9. Divide 347 and 459:
0.75599 x 100 = ?
10. Multiply 0.75599 by 100 to find the result.
0.75599 x 100 = 75.599 or 75.6 percent of predictive value of a negative result.
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