Reference no: EM131744714

Gas chromatography. Gas chromatography is a technique used to detect very small amounts of a substance, for example, a contaminant in drinking water. Laboratories use regression to calibrate such techniques. The following data show the results of five measurements for each of four amounts of the substance being investigated.²² The explanatory variable x is the amount of substance in the specimen, measured in nanograms (ng), units of 10^-9 gram. The response variable y is the reading from the gas chromatograph.

(a) Make a scatterplot of these data. The relationship appears to be approximately linear, but the wide variation in the response values makes it hard to interpret.

(b) Compute the least-squares regression line of y on x, and plot this line on your graph.

(c) Now compute the residuals and make a plot of the residuals against x. It is much easier to see deviations from linearity in the residual plot. Describe carefully the pattern displayed by the residuals.