Based in this exercise:

ANOVA problem:Five samples for each of four brands of chips were tested for sodium content, measured in milligrams of sodium per cup serving.

Brand 1	Brand 2	Brand 3	Brand 4
250	175	175	200
251	185	180	210
260	175	180	210
255	180	170	195
245	165	190	205

Using the ANOVA method at 0.05 significance level, test if there is a difference between the average sodium content of the different brands of chips.

Q: What is the independent variable?