Investigating Blue Nile's Claims on Buying Diamonds
A group project testing Blue Nile's own claims about what drives diamond price and appearance, against 1,214 diamonds pulled from their actual stock.
The claim under test
Blue Nile ranks the 4Cs — cut, color, clarity, carat — in that order for diamond appearance, and points to carat as the main driver of price. Four of us (Group 8, MATH 309 at JMU) pulled 1,214 diamonds from their live stock and checked whether their own inventory backs that up: what actually predicts price, and does the stock they carry match the priorities they preach.
What the stock says versus what the price says
Stock quantity told one story: Ideal cuts dominated the inventory regardless of color, clarity was spread evenly across grades, and cut and color held steady across carat weights — all consistent with cut mattering most for appearance. Price told a different one. Very Good cuts occasionally outpriced Ideal cuts, clarity barely moved price at all, and carat alone explained 89.6% of price variance in a log-transformed regression, with color as the clearest secondary driver.
The inventory backs the appearance claim.The pricing data backs a much simpler story: carat and color, mostly.