Experimental Design Statistics Example 4

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Example 4

hard
Design a double-blind experiment to test whether caffeine improves reaction time. Specify: (a) how participants are assigned, (b) what the treatment and control conditions are, (c) what 'double-blind' means and why it matters, (d) the response variable.

Solution

  1. 1
    Step 1: (a) Randomly assign participants to two groups. (b) Treatment: drink containing caffeine. Control: identical-tasting drink without caffeine (placebo). (c) Double-blind means neither the participants nor the researchers measuring reaction time know who received caffeine. This prevents bias in measurement and the placebo effect.
  2. 2
    Step 2: (d) The response variable is reaction time, measured in milliseconds using a standardised test. Faster reaction time in the caffeine group (with statistical significance) would support the hypothesis.

Answer

(a) Random assignment to two groups. (b) Treatment: caffeinated drink; control: identical placebo. (c) Double-blind: neither participants nor testers know assignments — prevents placebo effect and measurement bias. (d) Response variable: reaction time in milliseconds.
Double-blind experiments provide the strongest evidence for treatment effects because they eliminate both participant expectations (placebo effect) and researcher bias in measurement. Combined with random assignment, this design isolates the true causal effect of the treatment.

About Experimental Design

Experimental design is the careful planning of experiments to establish cause-and-effect relationships by controlling variables, using comparison groups, and randomly assigning subjects to treatment and control conditions to isolate the effect of interest.

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Example 3 medium

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