Overview of the Scientific Method

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

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”

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

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

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

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

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.

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

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

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 email so sample is biased - lower economic groups may not have access; elderly may not have email Interested in all voters, but call home at 1pm Monday – Friday. Why might this create a biased sample?

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?

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?

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)

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

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

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?

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

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