Exercise 3: Designing a Simple Controlled Experiment — Possible Solution
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This exercise has no single correct topic - the point is correctly
identifying all three real variable types for a genuine experiment. A
worked example, testing whether background music affects study
performance:

INDEPENDENT VARIABLE: whether a participant studies with background
instrumental music playing or in silence - the specific condition
being deliberately varied between the two groups.

DEPENDENT VARIABLE: the participant's real score on a standardized
quiz covering the material studied, taken immediately afterward - the
measured outcome used to compare the two groups.

CONTROLLED VARIABLES:
1. Study material - both groups study the exact same real text, for
   the same amount of information covered, so neither group has an
   inherently easier or harder task.
2. Study duration - both groups get the identical real amount of time
   to study (e.g., exactly 20 minutes), so neither group benefits from
   extra time.
3. Testing conditions - the quiz itself is taken under the same real
   conditions for both groups (same room type, same time limit, same
   quiz questions), so the comparison isolates the music variable
   specifically.

With participants ideally randomly assigned to the music or silence
condition (per this chapter's own randomization principle), this
design would let a real difference in average quiz scores be
attributed to the music condition specifically, rather than to
differences in material, time, or testing conditions.

ANSWER: (worked example) Independent variable: background music vs.
silence while studying. Dependent variable: quiz score on the studied
material. Controlled variables: identical study material, identical
study duration, and identical testing conditions for both groups -
isolating the music variable as the real explanation for any
difference in outcomes.

WHY THIS WORKS AS AN ANSWER
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This designs a genuine, real experiment with all three variable types
clearly and correctly identified, matching the exact structure taught
in the chapter's own Lind example.