Final answer:
The independent variable is the brand or price of dog food and the dependent variable is the dogs' lifespan. Researchers would study changes in the dogs' lifespan based on the dog food brand to determine a potential relationship.
Step-by-step explanation:
In the context of the student's question, the independent variable would be the brand of dog food. More specifically, it refers to the difference in price (expensive vs. less expensive) of the dog food brands being investigated. The dependent variable would be the lifespan of the dogs. You would hypothesize whether or not the consumption of more expensive dog food affects the lifespan of dogs, expecting to observe changes in the dependent variable based on variations of the independent variable.
When conducting scientific research, it is critical to identify the independent variable as the cause or condition you manipulate and the dependent variable as the effect or outcome that you are measuring. This helps in understanding the potential relationship between two variables and testing it through reliable methods.