Experimental Design

Experimental method

  • Looking for causal relationship
  • Manipulate one variable (independent variable) to measure effects on anther variable (dependent variable)
  • Operation definitions → make variables quantifiable
  • Must pick population → use random sampling
  • Experimental group: receive “treatment” → vary the IV
  • Control group: “normal” group

Random assignment: after random sampling, randomly assign participants to control or experimental group

  • Minimize pre-existing differences/confounding variables

Confounding variable: any other variable other than the IV that might affect the dependent variables

Experimenter bias: expectation of experimenters causes them to treat subjects in two groups different which affects results

  • Double-blind procedure: neither experimenters nor participants know who is in the control vs. experimental group
    • Lessens participant and experimenter bias

Participant bias: expectation of participants knowing they’re in the control group or not causes them to act differently which affects results

  • Placebo effect: people who believe they are receiving treatment will act as if they did receive the treatment; response to inert substance or nonspecific treatment (placebo) due to subject’s expectations

Ethics

APA Ethical Guidelines for Human Research

1) Informed consent

  • Must know they are subjects and agree to being a subject

2) Deception

  • Allowed if study cannot be performed without it
  • Must be careful about potential trauma caused by it

3) Coercion

  • Cannot force someone to be a subject

4) Anonymity

  • Cannot disclose personal details of subjects

5) Risk

  • Cannot be significant long term risks to subjects (physical/psychological)

6) Debriefing

  • Explains the true purpose of the study immediately after the study is complete
  • If there is deception, subjects must be informed afterwards

APA Guidelines for Animals in Research

1) Purpose

  • Must of clear scientific purpose

2) Care

  • Must be fed and housed properly

3) Legally acquired

4) Suffering

  • Must minimize

International Review Board (IRB): reviews ethics of proposed human experiments at research institutions or universities

IACUC: Institutional Animal Care and Use Committee