The design phase of a product development project will determine 70% to 90% of the product's ultimate development, consumer, and support costs and over its lifetime... and, if executed correctly, may well uncover the vast majority of problems that would eventually be encountered with the product should such a review never take place. Also it's estimated that at least 50% to 70% of cost reduction opportunities exist within the design phase.

For corroborating evidence see:

"Reviews in the first 15% of a product development project's time frame stand to eliminate 95% of the problems!"¹

"The cost structure of a product is determined when a product specification is completed, 80% to 90% of the product's lifecycle costs are locked in, leaving only 10% to 20% of the cost to be managed after the product is released." ²

"80 % of a product's cost is determined at the design phase." ³

"With 80 percent of supply chain costs determined during product definition, better collaboration across global design chains shortens cycle times and creates huge business impact." ⁴

"Studies reveal that around 70% to 80% of the cost of a product is decided in the design phase (Andreason et al ., 1983a; Corbett 1986; Whitney 1988; and Vogt 1988). The remaining 20% to 30% of the cost is determined during actual production." ⁵

"In most industries, 70% to 80% of product cost is determined in the design stage. So, it is critical to maximize the efficiency of the product development process." ⁶

"The decisions made by the end of this (design) stage will determine the product cost, design, manufacturing, test and service complexity and will also determine how difficult it will be to ramp production. Unless the product is completely redesigned, 80% to 90% of the product cost is determined." ⁷

"It is estimated that over 80% of all product-related environmental impacts are determined during the design phase of a product." ⁸

¹http://www.goldensegroupinc.com/desrevmotiv-6.shtml
² "Product Strategies for High Technology Companies ", Michael E. McGrath.
³ "Identifying and removing error in hierarchical cost estimates ", D.A. Koonce, R.P. Gandhi, A.N. Nambiara and R.P. Judd
⁴http://www.microsoft.com/industry/manufacturing/hightech/solutions/newproductdevelopment.msp
⁵"Concurrent Engineering: Contemporary Issues and Modern Design Tools", H. R. Parsaei , William G. Sullivan
⁶http://www.ssaglobal.com/solutions/plm/pdm.aspx
⁷" Improving Product Reliability: Strategies and Implementation " Mark Levin, Ted T. Kalal
⁸The Eco-design Directive for energy using product; http://www.eceee.org/european_directives/Eco_design/