When we first looked at diamond prices (in For Example: "Diamond prices"), we noted that we needed to model prices for different coloured diamonds separately. In other examples, we restricted our attention to either the D- or K-colour diamonds at either end of the colour spectrum. Here's a scatterplot of Price vs. Carat Weight for the E- and F-colour stones:

QUESTION:

Which assumptions for linear regression are violated in this plot?

Price 10,000 8,000 6,000 4,000 2,000 0.4 0.8 1.2 Carat Weight