Lets analyze each option A Decaffeinated coffee consumption was the independent variable This is True The independent variable IV is the variable that is systematically manipulated or varied by the experimenter to see its effect on another variable Here the researchers are investigating the effect of decaffeinated coffee implying its the variable they are interested in changing or observing changes in its presenceamount B Test performance was the dependent variable This is True The dependent variable DV is the measurable behavior or outcome that is observed to change in relation to the independent variable The researchers measured test performance to see how it was affected by decaf coffee consumption C The team effectively controlled for all extraneous variables influencing test performance This is NOT True It is practically impossible for researchers to control for all possible extraneous variables in any experimental design especially in studies involving human behavior in complex naturalistic settings like a school While researchers strive to minimize confounding variables through various control procedures eg random assignment holding conditions constant stating that all were effectively controlled is an unrealistic and unachievable claim Other factors like students study habits sleep quality prior knowledge or general health could also influence test performance and are difficult to completely control for D The researchers identified a correlation between decaf coffee and test scores This is True The statement the more decaf coffee students drink the better they scored describes a consistent relationship or trend between two variables This relationship is a correlation specifically a positive correlation It does not however imply causation To establish causation one would need more rigorous experimental control to rule out alternative explanations which is precisely why option C is false