Analyst Gene Munster of Piper Jaffray referred to the new index as "a pulse on what consumers are willing to pay for unsubsidized phones in the US." The index compares US eBay auction ending prices for the iPhone 5, iPhone 4S, iPhone 4, Galaxy S III and Galaxy Note II over a rolling 8 weeks to create a trend on resale prices.
"The key takeaway from 8 weeks of data is that the iPhone is holding slightly more of its value compared to the top two Galaxy phones," according to Munster. The iPhone 5's eBay auction ending value dropped about 11.2 percent in the last 8 weeks, while the comparable Samsung Galaxy S III dropped 13.7 percent in value.
The iPhone 4S kept its value the best, dropping only 7 percent during the same time period. The Galaxy Note II did the worst job of retaining its value, dropping a full 15 percent in just 8 weeks. Munster expects iPhone aftermarket prices to drop as the release of the next model of iPhone draws nearer.