Experimental Design and Factorial Designs Quiz

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Questions and Answers

What is the main purpose of random assignment in an experimental study?

To ensure that each subject gets a fair chance of being in either the experimental or control group (correct)
To guarantee a perfect match between the experimental and control group
To manipulate the dependent variable
To introduce bias into the study

Which threat to internal validity refers to the possibility that the observed differences between groups could be due to naturally occurring events rather than the treatment?

Maturation
Instrumentation
Statistical Regression to the Mean
History (Coincidental Events) (correct)

In an experimental study, what does the control group typically receive?

A placebo with no active ingredients
The same as the experimental group
No treatment or a neutral treatment (correct)
The treatment being tested

What is the purpose of selecting subjects that are representative of the population of interest in an experiment?

To make sure the study results can be generalized to the population (C) Signup and view all the answers

Which factor contributes to threats to internal validity by causing changes in participants over time, unrelated to the treatment?

Maturation (C) Signup and view all the answers

What is one of the key differences between external and internal validity in experimental research?

External validity refers to how well findings apply to other populations, while internal validity is about causality within a study. (A) Signup and view all the answers

What is the primary purpose of using a control group in an experiment?

To ensure equivalence between the two groups on the dependent measures (C) Signup and view all the answers

Why do we randomly assign subjects in an experiment?

To help ensure equivalence between the two groups on dependent measures (C) Signup and view all the answers

What is a key reason for using a pretest in an experiment?

For baseline data to calculate pretest/posttest delta (A) Signup and view all the answers

Why do experimental groups receive treatments in an experiment?

The experimental group gets the treatment (C) Signup and view all the answers

Which group receives something unrelated to the dependent variable in an experiment?

Control Group (A) Signup and view all the answers

What is a primary reason for using a posttest in an experiment?

To measure the delta between the pretest and posttest (C) Signup and view all the answers

What is the purpose of using a control group in an experiment?

To create a baseline for comparison with the experimental group (A) Signup and view all the answers

Why is it important to limit the duration of a study?

To prevent maturation effects from impacting the results (D) Signup and view all the answers

What is the main concern with subjects dropping out during an experiment?

It can impact the external validity of the study (C) Signup and view all the answers

Why is random assignment of subjects important in an experiment?

To reduce selection bias and increase internal validity (D) Signup and view all the answers

How does using a control group help address threats to internal validity?

By providing a comparison point to assess the impact of the treatment (B) Signup and view all the answers

What is one way to enhance external validity in an experiment?

Ensuring that subjects represent a diverse population (B) Signup and view all the answers

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Study Notes

Experimental Design

To measure the delta between groups on the posttest, a pretest and posttest are used to determine the effect of the treatment.
Random assignment of subjects is used to reduce threats to internal validity and ensure equivalence between the two groups.

Threats to Internal Validity

History (Coincidental Events): events outside the experimental treatment that occur at the same time as the study.
Experimental Mortality (Attrition): when subjects drop out during the study, and those who drop out are different from those who remain.
Statistical Regression to the Mean: when subjects are chosen due to extreme scores on a test, they are likely to score closer to the mean on a retest.
Maturation: subjects naturally mature during the course of a long experiment.
Instrumentation: differences between the pretest and posttest due to a lack of reliability in measurement.
Testing: effects of taking the pretest and posttest on the dependent variable.
Selection (Assignment): the process of assigning subjects to the experimental or control group.
Diffusion: when the treatment group shares information with the control group.

Experimental Design Strategies

Use a control group to help reduce threats to internal validity.
Use random assignment of subjects to ensure equivalence between the two groups.
Use a pretest to test for equivalence of the groups at the start and for baseline data.
Use a posttest to measure the delta between the pretest and posttest.
Include a delayed posttest to determine if the effects are lasting or fade quickly.
Limit the duration of the study to reduce the impact of external events.
Plan carefully to avoid external events that may impact the groups differently.
Use groups that are close in time, space, etc. to reduce the impact of external events.

Experimental Design Prevention

Use a control group to prevent threats to internal validity.
Set clear expectations and get commitment to prevent attrition.
Keep the study short and relatively painless to prevent attrition.
Explain how those who dropped out are not different to prevent attrition.
Use a control group to prevent statistical regression to the mean.
Keep the study as short as possible to prevent statistical regression to the mean.
Use a control group to prevent maturation.
Use a control group to prevent instrumentation.