PMI Exam PfMP Topic 2 Question 71 Discussion

In a portfolio you have a continuous interaction between the portfolio and its components. The approach is top down when it comes to offering guidelines and approaches and becomes bottom up when the components report status and progress to the portfolio. Metrics are used for measuring the performance. They need to be meaningful in order to be able to provide clear and logical targets, and in order to be able to be measured. Which guideline is used in order to develop meaningful measures?