Transcript variables
Experimental Design Showing Cause & Effect Relationships Experiments • 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., democratic vs. authoritarian classroom • The other is observed and measured – e.g., cooperative behavior among students Definitions • Hypothesis—A testable prediction of the outcome of the experiment or research • Variables—factors that change in ways that can be observed, measured, and verified • Operational definition—precise description of how the variables will be measured Operational Definitions • How the researcher will define and measure the key variables in the experiment. • In evaluating others’ research, first determine if you agree with the researchers’ operational definitions. Experimental Group • The subjects in an experiment who are exposed to the treatment (independent variable) • Also called the experimental condition • The group being studied and compared to the control group Control Group • Are not exposed to the independent variable • Results are compared to those of the experimental group • Also called the control condition Experimental Variables • Independent variable (IV) – the controlled factor in an experiment – hypothesized to cause an effect on another variable • Dependent variable (DV) – the measured facts – hypothesized to be affected Independent Variable • The experimental variable which causes something to happen • The “cause variable” • The variable manipulated by the experimenter • The variable which should change the dependent variable Dependent Variable • The experimental variable which is affected by the independent variable • The “effect variable” • The outcome of the experiment • The variable being measured Knowing the Difference • Use an If/Then Statement • If this (independent variable) THEN this happens (dependent variable). • If my subject drinks an energy drink (Ind. Variable) THEN they should get a surge in energy (Dep. Variable) 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 & bias Limitations of Experiments Flaws to Look Out For Limitations of Experiments • Often criticized for having little to do with actual behavior because of strict laboratory conditions • Ethical considerations in creating some more “real life” situations Confounding Variables • Variables, other than the independent variable, which could inadvertently influence the dependent variable • These variables should be controlled for in order to draw a true, cause-effect relationship in the experiment. • Many confounding variables can be eliminated through random assignment. Confounding Variables: Environmental Differences • Any differences in the experiment’s conditions--between the experimental and control groups • Differences include temperature, lighting, noise levels, distractions, etc. • Ideally, there should be a minimum of environmental differences between the two groups. Confounding Variables: Expectation Effects • Any changes in an experiment’s results due to the subject anticipating certain outcomes to the experiment • Change in DV produced by subject’s expectancy that change should happen Sources of Bias • Demand characteristics—subtle cues or signals by the researcher that communicate type of responses that is expected. Control of Bias • Placebo control group—exposed to a fake IV (placebo), the effects of which are compared to group receiving the actual IV. Placebo • A non-active substance or condition administered instead of a drug or active agent • Given to the control group • Reduces expectancy effects • Ever get a boo boo and have your mom or dad to kiss it and make it better? • Doctors may use Placebos more than you think (NBC Report on Placebo 2 min.) Placebo Effect • Play “The Placebo Effect: Mind-Body Relationship” (9:14) Segment #3 from The Mind: Psychology Teaching Modules (2nd edition) – Placebo Effect in Patients with pain medication is looked at. – “Nocebo” – Patients when told a drug won’t work can block it from working. Blind procedure • An experimental procedure where the research participants are ignorant (blind) to the expected outcome of the experiment • Sometimes called single blind procedure Double Blind Procedure • Technique in which neither the experimenter nor participant is aware of the group to which participant is assigned Experiments: Data Analysis Statistically Significant • Possibility that the differences in results between the experimental and control groups could have occurred by chance is no more than 5 percent • Must be at least 95% certain the differences between the groups is due to the independent variable Experiments: Replication Replication • Repeating the experiment to determine if similar results are found • If so, the research is considered reliable. • Does Vitamin C really prevent colds? Experimental Method • Play “Water, Water Everywhere” (12:20) Segment #2 from Scientific American Frontiers: Video Collection for Introductory Psychology (2nd edition) – Dousing Rods to find water – An experiment is set up to see if this psychic phenomenon is true.