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Research Methods in Psychology

Experiments Continued

Within Subjects

  • Definition of Within Subjects Design: A study where the same people participate in all conditions of the experiment. This helps researchers compare results fairly because they are looking at the same individuals.

Threats to Internal Validity

  • Overview of Internal Validity: This is about making sure that the only thing causing a change in your results is what you intentionally changed in your experiment (the independent variable), and not something else you didn't control.

Between Subjects Design

Hypothesis Example

  • Hypothesis examined: We are testing if combining pop-rocks and soda causes a stomach explosion.

Overview of Between Subjects

  • Description of Between Subjects Design: This involves comparing different groups of people, where each group experiences a different situation or condition.

  • Example Conditions:

    • Just SODA

    • Just CANDY

    • SODA + CANDY

Discomfort Scale

  • Explanation of the Discomfort Scale: Participants report how much discomfort they feel after consuming soda, candy, or both. This helps evaluate our idea about stomach discomfort.

Key Reasoning

  • Conclusions about discomfort are based on comparing measurements across these different groups, for example, claiming combined ingredients caused more stomach discomfort.

Within Subjects Design Characteristics

Reasons for Using Within Subjects

  • Addressing Random Assignment Issues: Sometimes, randomly putting people into groups doesn't perfectly create equal groups. Using the same people in all conditions helps control for differences between individuals.

  • Example Group Designation:

    • The same person would experience SODA

    • The same person would experience CANDY

    • The same person would experience SODA + CANDY

Explanation of 'Within Subjects'

  • This term refers to looking at how results (dependent variable scores) change for the same individuals under various conditions or at different times.

  • In research, this is often called a correlated groups design because we measure the same group of individuals multiple times, so their scores are


Research Methods in Psychology

Experiments Continued

Within Subjects Design

In a Within Subjects Design, we study the same group of people under all the different conditions of our experiment. This is helpful because by using the same individuals throughout the study, we can be more confident that any changes we see are truly due to what we are testing, rather than differences between different groups of people.

Threats to Internal Validity

Internal Validity is extremely important. It's about making sure that the only thing causing a change in your experiment's results is the specific factor you are trying to test (the independent variable). We want to be certain that outside factors aren't secretly influencing our findings.

Between Subjects Design

Hypothesis Example

Let's consider an idea: We want to see if mixing pop-rocks and soda together will cause a stomach explosion.

Overview of Between Subjects

A Between Subjects Design works by comparing different groups of people, where each group experiences only one specific situation or condition related to the experiment. For our example, we would have separate groups:

  • One group would only consume SODA.

  • Another group would only consume CANDY.

  • A third group would consume SODA + CANDY.

Discomfort Scale

To measure our findings, we would ask each participant to rate how much stomach discomfort they feel after consuming their assigned item(s). This is our "Discomfort Scale" and it helps us understand if one condition causes more discomfort than others.

Key Reasoning

Our conclusions about stomach discomfort would then come from comparing the average discomfort levels reported by these different groups. For instance, if the "SODA + CANDY" group reported much higher discomfort, we might conclude that the combination caused more stomach issues.

Within Subjects Design Characteristics

Reasons for Using Within Subjects

Sometimes, even when we try to create groups randomly, there can still be small differences between the people in each group. Using a Within Subjects Design helps avoid this problem because the same person acts as their own comparison across all conditions. This means individual differences don't get in the way of our results. For example:

  • The same person would first experience SODA.

  • Then, that same person would experience CANDY.

  • Finally, that same person would experience SODA + CANDY.

Explanation of 'Within Subjects'

This term specifically means we are looking at how a person's results (their scores on the dependent variable) change as they go through different conditions or at different times. In research, this is also often called a correlated groups design because we are measuring the same individuals multiple times, and because it's the same person, their scores are naturally connected or "correlated" to each other.