【正】 Vehicle Dependability Index Study(VDI) This study provides a problem measurement and diagnostic system similar to that of our Initial Quality Study (IQS). VDI is desired to capture information on the quality problems of two-to four-year old vehicles. While it closely follows the IQS design, VDI replaces problems that occur dung production and shipment, such as dents and dings, with longer term problems such as rust and corrosion.