1. Overview of the Scientific Method

2. The Experiment Research Method
an investigator manipulates one or more factors (independent variables) to observe their effect on some behavior or mental process (the dependent variable)
by random assignment of participants the experiment controls other relevant factors

3. The Experiment
An experiment involves a set of controlled conditions that aims to confirm a hypothesis
Hypothesis refers to a statement of cause and effect:
“Higher environmental temperatures lead to more aggression”
“Exposure to marijuana increases appetite”

4. The Experiment
Direct way to test a hypothesis about a cause- effect relationship between factors
Factors are called variables
One variable is controlled by the experimenter
e.g., amount of skittles eaten daily
other examples?
The other is observed and measured
e.g., the amount of weight gained

5. Experimentation Independent Variable
the experimental factor that is manipulated
the variable whose effect is being studied
The manipulated factor in an experiment
hypothesized to cause an effect on another variable
Dependent Variable
the experimental factor that may change in response to manipulations of the independent variable
in psychology it is usually a behavior or mental process
the measured facts
hypothesized to be affected

6. Experimental Variables
To test a hypothesis, an experimenter defines the variables of the hypothesis:
Cause: Independent variable (IV)
Marijuana: Plain cigarette versus cigarette containing 5 mg of THC (the active ingredient in marijuana)
Effect: Dependent variable (DV)
Appetite: Grams of ice cream consumed in 1 hour
The experimenter manipulates the IV and measures the DV to test the hypothesis

7. Experimentation Experimental Condition – Gets the IV/treatment
the condition of an experiment that exposes participants to the treatment, that is, to one version of the independent variable
Control Condition- Gets nothing (placebo)
the condition of an experiment that contrasts with the experimental treatment
serves as a comparison for evaluating the effect of the treatment
Placebo
an inert substance or condition that may be administered instead of a presumed active agent, such as a drug, to see if it triggers the effects believed to characterize the active agent

8. Control Group Controls are important for determining causality
The only difference between the experimental and control groups is the presence or absence of the IV.

9. The Experimental Model
Experimental Group
Receives the treatment (Independent Variable-IV)
Outcome (Dependent Variable-DV)
Control Group
Receives no treatment or the placebo
Outcome

10. Experimental Design
Random sample - every member of the population being studied should have an equal chance of being selected for the study
Random assignment - every subject in the study should have an equal chance of being placed in either the experimental or control group
Randomization helps avoid false results

11. Sources of Bias Biased sample –
when the members of a sample differ in a systematic way from the larger population in which the researcher is interested
Example
interested in all voters, but contact by so sample is biased - lower economic groups may not have access; elderly may not have
Interested in all voters, but call home at 1pm Monday – Friday. Why might this create a biased sample?

12. Sources of Bias
Experimenter bias refers to expectations that influence subject behavior
Observer-expectancy effect
researcher has expectations that influence measurements
Subject-expectancy effect
subject knows design and tries to produce expected result
How could either or both be prevented?

13. Preventing Bias: BLINDING
minimize expectancy by removing knowledge about experimental conditions
Single-blind study - when subjects are kept uninformed as to the treatment they are receiving
Double-blind study - when both subjects and experimenter are kept uninformed about aspects of the study that could lead to differential expectations
Which would create the stronger study and why?

14. Placebo Effects
Placebo effects represent changes in behavior that are related to expectations of a treatment
Placebo effects are controlled by a blind control group (the subject does not know whether the treatment was given or not)

15. All 4s…
Describe (3) sources of bias and (2) ways to eliminate bias in an experiment

16. CONFOUNDING VARIABLE
Other influences BEYOND the control of the research that may contribute to the dependent variable effects
Clothing & Popularity
Hair length & Confidence

17. Frequently Asked Questions about Psychology: Ethics
Why do psychologists study animals? Is it ethical to experiment on animals? Is it ethical to experiment on people?

18. Ethical Issues in Research
Respecting the rights of human research participants involves:
Informed consent is an explanation of a study and the responsibilities of experimenter and participant
Deception involving the subjects must be justified
Confidentiality of study information must be maintained
Debriefing refers to explaining the research process to the subjects at the end of the study
Animal research must be justified and must minimize discomfort to participants

19. Ethical Issues in Psychological Research
Right to privacy
Informed consent
use of deception
Animal rights
Is there justification for discomfort or harm a research procedure may produce?
APA publishes ethical guidelines