How much of market trend data is used for pro-forma statement

[Vijay Kurhade]

First of all, Wishing every one Merry Xmas and Happy Safe Holidays!

For development project pro-forma of any type residential/commercial/industrial/...., is market trend data referred for financials both cost and earnings, project duration by feasibility experts team; or it is industry experience of Developer who provide this data.

What is industry practice? use market trend data or developers use their own data from experience?

thanks in advance