Final answer:
In studies like the one described, Roger's diet (consumption of granola bars) serves as the independent variable, whereas in the scenario with ten-year-old boys eating doughnuts, the weight gained is the dependent variable because it is what's being measured in response to the introduction of the independent variable.
Step-by-step explanation:
Understanding Independent and Dependent Variables
In the context of the question provided, if a study were to be conducted to assess the effect of Roger's diet, specifically his consumption of granola bars, on some measurable outcome, the independent variable would be Roger's diet. For instance, if the study aims to understand the impact of granola bars on Roger's health or academic performance, researchers would manipulate or observe Roger's granola bar intake as the independent variable. An independent variable is a factor or condition that is intentionally changed by scientists or researchers to observe its effect on the dependent variable.
In an experiment, such as the one where ten-year-old boys are fed doughnuts to see how much weight they gained, the dependent variable would be the weight gained, as it is the variable that is expected to change as a result of the manipulation of the independent variable (the doughnuts).
Thus, to answer the given scenario, the weight gained is the dependent variable, as it is the outcome that the researchers are measuring.