Selecting an Experimental Design - AP Statistics

What is the main purpose of blinding in experiments?

To prevent bias in treatment administration and assessment. Eliminates placebo effects and experimenter bias.
In a randomized block design, what is the block?

A group of subjects that are similar in ways expected to affect the response. Homogeneous units within blocks reduce experimental error.
What is an independent variable in an experiment?

The variable that is manipulated by the researcher. The factor deliberately changed to test its effect.
Which design is preferable for a small sample size?

Matched pairs design. Maximizes statistical power when subjects are limited.
What differentiates a quasi-experiment from a true experiment?

Lacks random assignment of subjects to treatments. Cannot randomly assign subjects to treatment conditions.
Choose the best design for testing interaction effects of multiple factors.

Factorial design. Can detect how factors combine to affect outcomes.
What is the primary reason for replication in experiments?

To increase reliability and accuracy of results. Multiple trials reduce impact of random variation.
Which method helps reduce sampling variability in experiments?

Replication. Multiple subjects per treatment reduce random variation effects.
In which design are subjects their own control?

Crossover design. Each subject receives all treatments as their control.
Define carryover effects in experimental design.

Effects of a previous treatment that influence outcomes in subsequent treatments. Previous treatments may affect responses to later treatments.
Identify the main advantage of a crossover design.

Each participant receives multiple treatments, reducing variability. Each subject serves as their own control group.
Which design is best for minimizing the impact of confounding variables?

Randomized controlled trial. Random assignment isolates treatment effects from confounders.
What is an advantage of a double-blind study?

Eliminates bias from both participants and researchers. Neither group knows treatment status, preventing bias.
Identify the key benefit of using a control group.

To isolate the effect of the independent variable. Shows changes due to treatment, not other factors.
What is the purpose of control groups in experiments?

To serve as a baseline for comparison to the treatment group. Establishes what happens without the experimental treatment.
What is the Hawthorne effect?

Subjects change their behavior because they know they are being studied. Awareness of observation changes natural behavior patterns.
How does blocking improve experimental design?

Reduces variability by grouping similar experimental units. Grouping similar units decreases experimental error.
What is the main limitation of observational studies?

Cannot establish causation due to lack of control over variables. Missing manipulation prevents proving causation exists.
What is the role of replication in a factorial design?

To assess the consistency of interaction effects. Multiple replications verify interaction effect reliability.
In which scenario is a matched pairs design most useful?

When comparing two treatments with closely related subjects. Pairing controls for individual differences between subjects.
What is the difference between a single-blind and double-blind study?

Single-blind: participants unaware of treatment. Double-blind: both participants and experimenters unaware. Prevents bias from expectations affecting results.
Identify the primary goal of randomization in experiments.

To eliminate bias and balance unknown factors. Random assignment distributes unknown confounders equally across groups.
Identify the role of random assignment in experimental design.

To ensure each participant has an equal chance of receiving any treatment. Creates comparable groups to isolate treatment effects.
What is a matched pairs design?

A design where subjects are paired based on similarities and given different treatments. Reduces variability by controlling for subject characteristics.
What is a response variable?

The variable measured as the outcome of the experiment. The outcome measure affected by the independent variable.
What is a confounding variable?

A variable that influences both the dependent and independent variables, causing a false association. Creates spurious relationships between variables being studied.
What is a placebo?

A substance with no therapeutic effect used as a control in testing new drugs. Controls for psychological effects of receiving treatment.
Define a block design in experiments.

Subjects are divided into blocks based on a characteristic, then randomized within blocks. Controls for known sources of variation before randomization.
Identify a key feature of a randomized controlled trial (RCT).

Subjects are randomly assigned to treatment and control groups. Gold standard design for establishing causal relationships.
What is an observational study?

A study where researchers observe subjects without manipulating variables. Cannot establish causation, only associations between variables.
What is an interaction effect?

When the effect of one factor depends on the level of another factor. Combined factor effects differ from individual effects.
What is a completely randomized design?

An experimental design where subjects are randomly assigned to treatments. Ensures each subject has equal probability of any treatment assignment.
What distinguishes an experiment from an observational study?

Experiments involve the manipulation of variables; observational studies do not. Only experiments can establish cause-and-effect relationships.
Which design reduces variability due to known confounders?

Randomized block design. Blocking controls known sources of variation.
Identify the essential feature of a crossover design.

Participants receive all treatments in a sequence. Same subjects receive all treatments over time.
Identify one disadvantage of a completely randomized design.

Less effective if there is variability among experimental units. Cannot control for differences between experimental units.
What is the primary purpose of a pilot study?

To test the feasibility and refine the study design. Identifies problems before conducting the full study.
What is an extraneous variable?

A variable not of interest but could affect the outcome. Must be controlled to avoid confounding the results.
What is the main challenge of a crossover design?

Potential carryover effects between treatments. Previous treatments may influence subsequent treatment responses.
Define a factorial design.

An experiment where two or more factors are tested simultaneously. Tests multiple factors and their interactions simultaneously.

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