In an investigation of the effects of caffeine on concentration,half the participants were given regular colas which contained caffeine and half were given decaffeinated colas.In this study,the decaffeinated colas are being used as

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Decaffeinated colas are being used as a placebo - a substance that has no physiological effect but is given to participants to control for the psychological effects of believing they are receiving an active substance. By using decaffeinated colas as a control, researchers can compare the effects of caffeine on concentration to the effects of simply believing that one has consumed caffeine (which may have its own cognitive effects).

In an Investigation of the Effects of Caffeine on Concentration,half