Jeffrey wants to lose weight by using caffeine to
help with exercise. He asks himself, Which
caffeine drink will raise the heart rate the most?"
He tries to test this out by comparing the heart
rates of his neighbors, 3 brothers who are
triplets. One of the brothers drinks Pepsi,
another drinks a double shot of espresso (which
is coffee with twice the normal amount of
caffeine) and a third brother drinks only water for
comparison.
Jeffrey finds out that the triplet with the double
shot of espresso had the highest heart rate.
4. What is the independent variable for this experiment?

The independent variable for this experiment is the amount of caffeine because there is no effect on the caffeine in the experiment while on the other hand, weight loss is dependent variable which affects due to the amount of caffeine. Independent variable are those which can't depend on any variable in the experiment and can stay independently. There is no effect on the amount of caffeine so we can say that it is an independent variable.