Worked examplesThree real selecting an experimental design questions
From the practice pool, not the mock papers — each with the reasoning that produces the answer.
100% of them come with a figure. Reading the graph or diagram correctly is most of the work here before any content knowledge applies.
100% test a single AP skill: Selecting Statistical Methods. That makes this topic unusually predictable to prepare for.
Selecting Statistical Methods · with figure
A community greenhouse alpha cycle expects bench to strongly affect seedling survival. Researchers randomly assign treatments separately within each bench. Which design principle is being used?
- AVoluntary response through the shade cloth.
- BA census with no treatment assignment.
- CBlocking on bench before random assignment.correct
- DCluster sampling of only one bench.
- EA large convenience sample removes selection bias because increasing sample size alone makes the sample representative.
Why C is correct
This uses blocking because random assignment occurs separately within levels of bench, a variable expected to affect seedling survival.
Blocking by bench in community greenhouse alpha cycle: the important cue is the community greenhouse alpha cycle setting. Match the method to the way the data are collected or the statistic is computed, then state the conclusion in the language of the stem.
Selecting Statistical Methods · with figure
The museum education program alpha cycle compares two versions of a gallery map. Each participating visitor tries both versions in random order, and audio-guide use is recorded after each version. What design is this?
- AA cluster sample of one grade band.
- BA large convenience sample removes selection bias because increasing sample size alone makes the sample representative.
- CA completely randomized design with separate unrelated groups only.
- DA voluntary response survey after seeing the gallery map.
- EA matched-pairs design using each participant as their own comparison.correct
Why E is correct
This is a matched-pairs design because the same participant experiences both versions, so comparisons of audio-guide use are made within participants.
Matched-pairs design for museum education program alpha cycle: the important cue is the museum education program alpha cycle setting. Match the method to the way the data are collected or the statistic is computed, then state the conclusion in the language of the stem.
Selecting Statistical Methods · with figure
A storm-drain survey alpha cycle expects street type to strongly affect leaf-litter depth. Researchers randomly assign treatments separately within each street type. Which design principle is being used?
- AVoluntary response through the measuring frame.
- BCluster sampling of only one street type.
- CA large convenience sample removes selection bias because increasing sample size alone makes the sample representative.
- DA census with no treatment assignment.
- EBlocking on street type before random assignment.correct
Why E is correct
This uses blocking because random assignment occurs separately within levels of street type, a variable expected to affect leaf-litter depth.
Blocking by street type in storm-drain survey alpha cycle: the important cue is the storm-drain survey alpha cycle setting. Match the method to the way the data are collected or the statistic is computed, then state the conclusion in the language of the stem.
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Last reviewed 2026-08-28. Topic and unit names follow the
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