Designs Unit 1

• Objectives and characteristics of the experimental method:

  • The experimental method involves following scientific guidelines to test hypotheses and establish causal relationships between variables
  • Experimental language includes terms like independent variable, dependent variable, and extraneous variable
• Main advantages of the experimental method:

  • Gives researchers a high level of control over the study
  • Experiments can be replicated due to standardized procedures
  • Allows cause and effect relationships to be determined
  • Conclusions of experiments allow useful applications to the real world
• Characteristics of the experimental method:

  • Manipulation involves purposefully changing something in the environment
  • Control is used to prevent outside factors from influencing the study outcome
  • Random assignment ensures equal chances for participants to be in different groups or treatments
• In a randomized and controlled psychology experiment:

  • Researchers examine the impact of an experimental condition on a group of participants
  • Experimental group receives the treatment or intervention of interest
  • Control group does not receive the experimental treatment for comparison
• Data variability and control techniques:

  • Control refers to removing the influence of extraneous variables on the dependent variable
  • Uncontrolled variables affect the reliability of arguments
  • Techniques are used to eliminate the differential influence of extraneous variables
• Components of total variance in an experiment:

  • Systematic Variance: related to variables under study and can be predicted by the researcher
  • Error Variance: portion of total variance that cannot be explained by the variables under study or by systematic factors
• MAXMINCON principle in experimental design:

  • MAXimize the systematic or desirable variance
  • MINimize the error variance
  • CONtrol the effect of extraneous variables
• MAXMINCON by Kelinger and Pedhazur (1973) and Kerlinger (1986):

  • MAXimizing the systematic or desirable variance
  • MINimizing the error variance
  • CONtrolling the effect of the extraneous variables
• To maximize experimental variance, researchers should make experimental conditions as different as possible
• Extreme values:

  • Refer to the minimum and maximum values of a given characteristic
  • For example, height measurements for the shortest and tallest people represent extreme values for the height characteristic
• Intermediate values:

  • Refer to the range of values between the minimum and maximum levels in an experimental study
  • For example, different doses of a medication on participants' cognitive performance can have intermediate values like low, medium, and high doses
• Control techniques to maximize systematic or desirable variance involve reducing the variability in the measurement of the dependent variable that is not attributable to the independent variable or other controlled factors
• To minimize error variance, researchers can employ strategies like standardized testing, random assignment, counterbalancing, and using reliable measurement tools
• Extraneous variables are factors other than the independent variable that can potentially affect the dependent variable and confound the results of an experiment
• Controlling for extraneous variables involves matching participants on relevant characteristics and holding variables constant across experimental conditions
• Common techniques to control extraneous variables include elimination, constancy, single-blind and double-blind studies, systematization of extraneous variables, and statistical control
• Blocking involves grouping participants into homogeneous subsets based on certain characteristics before assigning them to treatment conditions
• Counterbalancing within-subjects design involves exposing all participants to the same treatments to measure changes over time or resulting from different treatments
• Counterbalancing between-groups design involves each participant experiencing only one condition and comparing group differences between participants in various conditions