Within Subjects design, Internal Validity, Order effects

Name the 4 benefits of a within subjects design

1. Can study change or compare responses to stimuli

2. Effective for monitoring how the same individuals change overtime.

3. Greater statistical power ( easier to isolate the independent variable effects)

4. Requires fewer participants to achieve the same power.

Name the two negatives of a within subjects design

1. Poor external validity

2. Potential threats to internal validity

Name the 2 reasons why poor external validity is a problem for within subjects designs.

1. Because observed changes could be due to multiple exposures and not just the independent variable

2. Experiencing multiple levels of some of the variables is less common irl.

Simply list the threats to internal validity (5)

1. Attrition and Mortality

2. Instrumentation

3. History

4. Maturation

5. Testing effects

Describe attrition and mortality as a threat to internal validity.

Differential dropping of participants (Because of the treatment or independent variable)

Describe instrumentation as a threat to internal validity.

Threat due to changes in how the dependent variable is measured in the study.

What are some examples of what instrumentation can look like/

1. Raters becoming more refined in their observations

2. Differences in the administration of our measures.

What does instrumentation lead to?

Difficulty in establishing causality, because changes in measurement could be mistaken for the effects of the independent variable.

How do we control for instrumentation?

By measuring the independent variable the exact same way each time.

Describe history as a threat to internal validity.

Its a threat caused by an external event that potentially influences a participants behavior during a study.

Describe maturation as a threat to internal validity.

Its a threat due to long term or short term physiological changes within the participants that may influence the dependent variable.

Provide examples of maturation

Long term would be aging or becoming wiser, short term would be tiredness, boredom, or hunger during the study.

Describe testing effects as a threat to internal validity.

When participants take a test more than once their scores can change simply because they are getting used to the test.

What does testing effects lead ot in participants?

Them being able to remember their previous answers or figure out the studies purpose.

Name the 4 order effects

1. Practice

2. Fatigue

3. Carryover

4. Sensitization

Practice order effect

Participants appear to improve by the end of the study because they had practice completing the dependent variable measures and not because of experimental manipulation.

How to minimize practice effects

1. Provide participants with extensive training on the task before starting the actual study.

2. Do a trial run so the participants can learn and improve

Fatigue Effect

Participants performance deteriorates during the study because they become tired, bored, and or less enthusiastic

How to minimize fatigue effects

1. Make the tasks more interesting

2. Keep the tasks brief

3. Keep the tasks from being too taxing

Carryover Effect

Exposure to one treatment changes responses to another

How to minimize carryover effect

1. Increase the time between treatments

2. Use other strategies that clear the effect before exposing participants to the next condition.

Sensitization Effect

Each treatment makes the participants more likely to guess the research hypotheses and change their behavior accordingly.

How to minimize sensitization effect

1. Mislead them about the purpose of the study

2. Use other strategies that prevent participants from knowing what you are varying in your study.