On a recent vacation cruise, while snorkeling with my wife in Cozumel, the diamond in her wedding band unfortunately was dislodged and became one with the ocean floor. After futile efforts to find the lost diamond, it was evident to me that I needed to get her a replacement ring to lessen the pain of the loss. The lost diamond had a 32-year run, and its days were numbered when it met its match, the ocean.
I don’t recall how I chose that diamond 32 years ago. However, I am now older and perhaps wiser this second time around. I decided to do my homework and leverage my JMP savvy for my decision making process. To begin, I collected some data on diamond rings. Gemologists characterize a diamond using a rating system called the Four Cs. These stand for carat size, color, cut and clarity. The one “C” that is not included is cost, but that is the response that I wanted to understand by modeling it using JMP.
The carat size is a unit of weight where one carat is equal to 0.2 grams. The clarity scale is broken down into categories IF, VVS1, VVS2, VS1, VS2, SI1 and SI2, representing the ranges from internally flawless to slightly included. These inclusions affect the diamonds clarity because they interfere with the light as it passes through the stone. The color scale runs D, E, F for colorless and G, H, I, J, K for nearly colorless. Finally, the cut, which measures the precision of the cut with respect to the table and depth of the stone, is expressed on a grading scale of ideal, excellent, very good and good. The cut determines the brilliance of the diamond and how well it reflects light.
So after assembling my JMP table with data from 2,690 diamonds, I modeled the cost as a function of the Four Cs. You can download my JMP file from the JMP File Exchange. With a target cost in mind, I interacted with the JMP Prediction Profiler to see what options were available to me. As you can see from the Profiler, the carat size is the biggest driver of cost, so I locked into a 0.75 carat size diamond and then used the Profiler interactively to see how the other factors affected the price of the diamond. I've embedded the Flash version of my Profiler below, so you can try it out yourself. If you're not seeing the Profiler without having to scroll, you can either make your browser window larger or resize one of the Profiler graphs by grabbing a corner of the graph.
I discovered that I could probably obtain the same size diamond with an H color rating and VS2 clarity for $1,000 less than one with a G color rating and a VS1 clarity. After this exercise, I felt armed and ready to negotiate my new diamond purchase. I’ve also learned that it’s a good idea to remove the diamond ring before snorkeling.