A sports scientist conducts a study to investigate the effect of a new electrolyte supplement on endurance.
Group 1, consisting of trained marathon runners, consumed the electrolyte supplement at 6:00 AM in a temperature-controlled room set to 11∘C11^{\circ}\text{C}11∘C and completed a 10 km treadmill run.
Group 2, consisting of recreational sprinters, consumed a water placebo at 3:00 PM in a temperature-controlled room set to 29∘C29^{\circ}\text{C}29∘C and completed the same 10 km treadmill run.
Identify one variable that might have been a confounding variable in this study. Justify your answer.
689 exam-style questions on AQA A Level Psychology Scientific processes. Each one has a worked solution and a mark scheme showing where the marks go.