Experimental Research Designs in Psychology

Fundamentals of Research Design

  • Definition of Research Design:
      Research design refers to the specific methodology used to organize participants within a study into experimental and control groups. It is the framework that determines which participants are exposed to which conditions of the independent variable and the specific order of that exposure.

  • The Role of the Research Design:
      In the simplest terms, the design’s function is to assign-also known as "allocate"-participants to the various conditions of an experiment.

  • Experimental vs. Control Groups:

  - Experimental Group:
    In standard experiments, this group is typically exposed to the manipulated independent variable.

  - Control Group:
    For this group, the independent variable is held constant rather than manipulated.

  • Complexity of Conditions:
      While psychological experiments can involve multiple conditions, a simple experiment is defined by having only two conditions.

  • Alternative Terminology:
      Research design is frequently referred to as experimental design because this structure is unique to experimental research.

  • Primary Experimental Designs:
      There are three primary designs utilized in psychological research:

  - Independent measures:
    Different groups of participants are exposed to only one condition of the experiment.

  - Repeated measures:
    The same group of participants is exposed to every condition of the experiment.

  - Matched pairs:
    Participants are paired with another individual who shares similar characteristics, but each member of the pair is exposed to only one condition of the experiment.

  • Selection Criteria:
      The choice of a specific research design is contingent upon the nature of the topic being studied, as every design possesses distinct strengths and limitations.

Independent Measures Design

  • Core Characteristics:
      This design is characterized by having two or more distinct groups, such as the experimental group and the control group. Participants in this design are exposed to only one condition of the independent variable.

  • Advantages: Limiting Participant Bias:

  - The primary benefit is the reduction of participant-driven bias. Participants may sometimes deduce the aim or hypothesis of a study, leading them to change their behavior to either please the researcher or deliberately confound the results.

  - Demand Characteristics:
    This psychological term refers to the phenomenon where an experiment's design "demands" certain behaviors from participants.

  - Artefacts:
    If participants react to demand characteristics, the resulting data is considered an artefact. This means what appears to be an effect of thinking or behaving is actually a byproduct of the experimental design itself. Independent measures avoid this by keeping participants unaware of the alternative conditions.

  • Disadvantages: Participant Variables:

  - The trade-off for avoiding demand characteristics is the risk of participant variables. This means groups may differ in personal characteristics, abilities, or backgrounds.

  - If groups behave differently, it may not be due to the independent variable, but rather due to these innate differences between the participants in each group.

  • Extraneous Variables:
      Participant variables are a specific type of extraneous variable. An extraneous variable is defined as anything other than the independent variable(s) that might influence the dependent variable and its measurement.

  • Specific Examples of Participant Variables:
      In an experiment measuring short-term memory capacity, results could be skewed by:
      - Pre-existing individual differences in memory capacity.
      - The amount of sleep a participant had the night before.
      - What the participants ate for breakfast.

  • Mitigation Strategy: Random Allocation:
      To minimize the influence of participant variables, researchers use random allocation (or random assignment).

  - Allocation Defined:
    The process of organizing participants into different groups for the experiment according to the research design.

  - Mechanics of Random Allocation:
    Every participant has an equal chance of being assigned to either the experimental or the control condition.

  - Goal:
    This process aims to "balance out" participant variables across groups, lessening the potential for individual differences to skew the final results.

Repeated Measures Design

  • Core Characteristics:
      In a repeated measures design, the same individual participants are used in every condition of the experiment.

  • Advantages: Controlling for Variables:

  - This design is often selected when a researcher wants to strictly limit the influence of participant variables on results.
  - Factors such as intelligence, gender, or socioeconomic status (SES) can significantly impact findings in certain research topics. By using the same participants throughout, these variables are held constant.
  - Repeated measures control for participant variables more effectively than any other design. It is the logical choice when participant variables are likely to interfere with the data.

  • Disadvantages: Order Effects:

  - The most significant drawback is the emergence of order effects (also known as carryover effects). This occurs when participation in the first condition affects the participant's behavior or performance in subsequent conditions.

  - Types of Order Effects:
    - Practice (or Learning):
      Participants may perform better in later conditions because they have gained experience or learned the tasks during the first condition.
    - Fatigue (or Boredom):
      Participants may perform worse in later conditions due to tiredness or lack of interest resulting from repetitive testing.
    - Context:
      The experience of the first condition may influence how a participant interprets tasks in the second condition, particularly if they begin to guess the intent or aim of the study.

Strategies for Controlling Order Effects

  • Counterbalancing:
      This is a primary method for managing order effects in repeated measures designs.
      - Mechanism:
        If an experiment has two conditions, A and B, the participants are split. Half complete the conditions in the order AB, and the other half complete them in the order BA.
      - Effectiveness:
        Counterbalancing does not remove order effects; rather, it distributes them across both conditions. This ensures that any gains from practice or losses from fatigue affect the experimental and control conditions equally.
      - Random Assignment:
        It is vital to use random assignment to decide which participants follow the AB or BA sequence to maintain experimental integrity.

  • Additional Control Strategies:
      - Time Lags:
        Implementing a long enough duration between experimental conditions to allow the effects of fatigue or learning to dissipate.
      - Randomizing Stimulus Materials:
        Changing the materials used in each condition to prevent familiarity.
      - Randomizing Condition Order:
        Ensuring the presentation order of conditions is randomized for every individual participant.

Matched Pair Design

  • Core Characteristics:
      This design involves using different participants for each condition, but those participants are paired based on specific shared characteristics relevant to the study.

  • Matching Criteria:
      Relevant characteristics used for matching may include age, gender, intelligence, culture, socioeconomic status, or specialized background such as musical training.

  • The "Happy Medium":
      The matched pair design is often viewed as a balance between independent and repeated measures designs:
      - It accounts for participant variables by matching individuals on relevant personal traits.
      - It avoids order effects because each participant is only exposed to one condition of the independent variable.

  • Limitations and Challenges:
      - Labor Intensive:
        Matching participants is a significant amount of work, particularly when researchers attempt to match according to multiple criteria simultaneously.
      - Inexact Matching:
        It is nearly impossible to match two participants identically. The only exception to this is when researchers sample identical twins.

Check Your Understanding & Tasks

  • Task 1: Research Design Check:
      Complete the "Check your understanding" Google Form related to the topic of Research Design.

  • Task 2: Activity:
      Complete the "Sampling or Assignment (Allocation)?" activity posted on the Classroom page. Students should access their own copies to complete the work.

  • Peer Collaboration:
      Students are encouraged to discuss the material with peers. Engaging in discussion is emphasized as a way to increase thinking and learning outcomes.

  • Glossary of Terms:
      Students are reminded to continuously update and work on their personal glossary of psychological terms.