A nutritionist is curious about how the concentration of a vitamin supplement changes as a function of time (in hours) since a pill has been swallowed. The nutritionist measures the concentration for six hours after the pill was swallowed. He calculates the equation of the least-squares regression line as ŷ = 0.0093 – 0.00121x where ŷ is the concentration and x is the number of hours since the pill was swallowed. The graph shown is the residual plot for this model where the residuals are measured in parts per thousand.

Based on the residual plot, is the linear model appropriate?

No, there is no clear pattern in the residual plot.

Yes, there is no clear pattern in the residual plot.

No, there is a clear pattern in the residual plot, indicating that the linear model is not appropriate.

Yes, clearly the concentration of the vitamin decreases for the first three hours and then increases after that.