title: How to calculate NPV at base rate of 12%
body: <p>When at the base rate of q1, we have TP1, FP1, TN1, and FN1. SN1, SP1, and NPV1 then can be drived. For example, NPV1 = TN1 / (TN1 + FN1).</p>
  <p>Similarily, when at the base rate of q2, we have TP2, FP2, TN2, FN2, SN2, SP2, and NPV2.</p>
  <p>Question: how can we calculate the NPV at base rate of q （q=12%）?</p>
  <p>If we use SN1, SP1, and q=12%, we can get one value for the NPV at base rate of 12%.
  But if we use SN2, SP2, and q=12%，we will get another value for the NPV at base rate of 12%.
  Out of the two NPV at base rate of 12%, which one should we trust?</p>
  <p>Why does the formula of calcualting NPV at base rate of 12% not consider the original base rate (for example q1 or q2) that it is derived from?</p>