Psychological Experimentation

The Experimental Method: Discovering the Causes of Behavior Experiment: A controlled situation in which the researcher manipulates one variable to discover its effect on another variable, while holding all other conditions constant. Key Concepts

Hypothesis Expresses a relationship between two variables. A variable is anything that can vary among participants in a study. Participating in class leads to better grades than not participating.

Hypothesis Null vs. alternative hypothesis Alternative = states the effect you expect the independent variable to have on the dependent variable Null = states the LACK of effect of the independent variable on the dependent variable GOAL = TO REJECT THE NULL HYPOTHESIS

1. Define your population Population = the group you are interested in. – all humans? – people with depression? – adolescents?

2. Obtain a sample to study Sample – a subgroup of your population In order for results to be generalizable to a population (able to infer that it is true for all members of the population), you need to obtain a representative sample. Random sample – everyone in the population has an equal chance of being in your sample.

Sampling Identify the population you want to study. The sample must be representative of the population you want to study. GET A RANDOM SAMPLE (preferred method of sampling) Other forms of sampling are sometimes used

Random Assignment Once you have a random sample, randomly assigning them into groups (each subject has equal chance of being put in each group) helps control for confounding variables. Experimental Group ( group that is exposed to the independent variable) v. Control Group ( group that is not exposed to the independent variable) Group Matching = not completely random; sometimes used

3. Operationally define variables Definitions should be quantifiable when possible. Reduces subjectivity and expectancy effects.

Operational Definitions Explain what you mean in your hypothesis. How will the variables be measured in “real life” terms. How you operationalize the variables will tell us if the study is valid and reliable. Let’s say your hypothesis is that chocolate causes violent behavior. What do you mean by chocolate? What do you mean by violent behavior?

The Experimental Method: Discovering the Causes of Behavior Independent Variable: The variable that the researcher “manipulates”. “Manipulates” basically means that we assign different levels of the variable to different groups. For example: Suppose the independent variable is the amount of time students have to take a test. We can give one class 40 minutes and another 60 minutes. These are the levels of the time variable. Key Concepts

The Experimental Method: Discovering the Causes of Behavior Dependent Variable: This is an aspect of the participant’s behavior that the researcher records to see if it will be influenced by the independent variable. For example: In the test-taking situation, we could record how many questions each student got right. Number of correct answers would be the dependent variable. In everyday terms: Independent Variable = “Cause” Dependent Variable = “Effect” Key Concepts

The Experimental Method: Discovering the Causes of Behavior So if the students who get 60 minutes to take the test do better than those who get 40 minutes, we can say it was the time factor that caused this difference in performance, assuming… there were no other differences between the classes. Everything else must be “HELD CONSTANT”. Key Concepts

4. Manipulate the independent variable (control all other variables) This is easier said than done. – Confounding variables – variables in a study that are not controlled for, but are not the focus of the study; can affect results.

Beware of Confounding Variables If I wanted to prove that smoking causes heart issues, what are some confounding variables? The object of an experiment is to prove that A causes B. A confounding variable is anything that could cause change in B, that is not A. Lifestyle and family history may also effect the heart.

Experimenter Bias Another confounding variable. Not a conscious act – experimenter unwittingly influences the results. Prevent with Double-Blind Procedure.

Other Confounding Variables Placebo effect Order Effects

How do we control for confounding variables? Large sample size (more likely to be representative) Random assignment to groups (control and experimental) Blind Techniques – Single vs. double blind – Controls for expectancy effects – Placebos or sham treatment

5. Collect and analyze data Do basic statistics (mean, median, mode, standard deviation) to simplify data. Compare control and experimental groups. Run inferential statistical test (more on this later) – T test, chi squared, ANOVA

Experimental Method TheoryProblem Question Research Literature Develop Hypothesis Pos Neg Null Alternative

Experimental Method (cont’d) Design the Experiment Random Sampling Random Assignment Apply Double Blind Experiment Execute Control Group Experimental Group Placebo Independent Variable Dependent Variable Dependent Variable Collect Data

Experimental Method (cont’d) Collect Data Analyze Data Quantify Report Findings Quantify Replicate Theory Supported or Discredited By Research Reliability Validity NO Extraneous Intervening, Confounding Variables