Your international consultant firm publishes Tender Price Index (TPI) quarterly on its website. Janice Chan, the Project Manager of one of your developer clients, has observed that the percentage increase in the unit construction cost per Construction Floor Area (CFA) of residential development is significantly higher than the corresponding percentage increase in your company’s TPI in the past decade. She casts a doubt about the accuracy of your company’s TPI. Draft an email to Janice to explain the purposes of TPI and why there is a deviation between percentage changes in residential unit construction cost and TPI.