Data Collectionmedium
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A researcher studies whether afternoon coffee improves alertness using a crossover design. Each of 30 participants completes two tasks—an 'alertness task' (count backward from 100 by 3s in 60 seconds) and a 'focus task' (spot image differences in 60 seconds)—under two conditions: after drinking coffee and after drinking a placebo. All 30 participants do the alertness task after coffee on Day 1 and the focus task after placebo on Day 2. Results show significantly better performance in the coffee condition. Which confounding factor is most problematic?
A researcher studies whether afternoon coffee improves alertness using a crossover design. Each of 30 participants completes two tasks—an 'alertness task' (count backward from 100 by 3s in 60 seconds) and a 'focus task' (spot image differences in 60 seconds)—under two conditions: after drinking coffee and after drinking a placebo. All 30 participants do the alertness task after coffee on Day 1 and the focus task after placebo on Day 2. Results show significantly better performance in the coffee condition. Which confounding factor is most problematic?