Final answer:
We need to keep ingredients constant in experiments to ensure reproducibility, which allows other researchers to obtain the same results and verify the findings. It also helps to establish a clear cause-and-effect relationship between the independent and dependent variables through the use of experimental controls.
Step-by-step explanation:
We need to keep the amount of ingredients in our experiment constant to ensure reproducibility. This means that when other researchers try to replicate the study, they should be able to get the same results, if the experimental conditions are the same. This is a fundamental aspect of the scientific method and helps to build confidence in the study's findings. Keeping the ingredients constant is related to experimental controls, which are crucial in demonstrating the cause-and-effect relationship between the independent variable (the one changed by the researcher) and the dependent variable (the one observed or measured).
In the provided case, the psychologist's study on tableware size affecting food consumption, the independent variable is the size of the tableware, and the dependent variable is the amount of food consumed. The psychologist uses random assignment to control for lurking variables, ensuring that the only significant difference between groups is the size of the tableware. This design strengthens the evidence for a cause-and-effect relationship between the independent and dependent variables.