AP Psychology Research Methods

The Scientific Method

Theory: An integrated set of principles that organizes and predicts behavior.

Hypothesis: A testable prediction often implied by a theory.

Operational Definitions: Statements (descriptions) of the procedures used to define research variables.

Replication: Repeating the essence of a study, usually with different participants and in different situations.

Hindsight Bias: The tendency to believe, after learning the outcome, that you knew that was how it would turn out.

Goal of research: To describe, predict, & explain behavior.

I. Research that Describes only

Case Study: A descriptive technique in which one person is studied in depth in the hope of revealing universal principles.

Naturalistic Observation: Observing & recording behavior in naturally occurring situations without manipulating or controlling the situation.

Survey: A technique for obtaining self-reported attitudes or behaviors of people, usually by questioning a representative, random sample of them.

Population: All of the people in a particular group from which a sample may be drawn.

Random Sample: A subset of people who fairly represent the population because each person has an

equal chance of being selected. Using a random sample increases the generalizability

of study.

Simple Random Sampling - Randomly picking individual names
Cluster Random Sampling - Randomly picking naturally occurring groups of people (Homerooms)
Stratified Random Sampling - First dividing the population into groups and then randomly picking individuals from those groups (Race, gender, grade, etc)
Nonrandom Sampling - Not everyone in the population has an equal chance of being picked. Also called convenience sampling. Because of this there would be SAMPLE BIAS

Generalizability: The extent to which results of a study can be applied to the outside world.

False Consensus Effect: The tendency to overestimate the extent to which others share our beliefs and

behaviors.

Social Desirability Bias: Tendency of subjects to present themselves in a socially desirable light.

II. Research the Describes and Predicts Behavior

(Non-Experimental Designs)

Correlational Research: Research that seeks to measure the RELATIONSHIP between two variables without trying to determine causality or manipulating either of the variables.

Scatterplot: A graphed cluster of dots, each which represents the values of two variables. The slope of the dots represents the direction (+ or -) of the relationship while the amount of "scatter" suggests the strength of the correlation.

Correlation Coefficient: A statistical measure of the extent to which two factors vary together, and thus how well either factor predicts the other. The statistic is always between -1.00 and +1.00.

A Positive correlation coefficient means that as one variable increases, so does the other.

A Negative correlation coefficient means that as one variable increases, the other decreases (i.e., an inverse relationship).

Regardless of the strength of the relationship, correlations cannot tell us that one variable CAUSES changes in the other because:

1) Variable X could be affecting variable Y OR variable Y could be affecting variable X.

2) Third variables could be affecting BOTH variables X and Y.

Illusory Correlation: The perception of a relationship between two variables where none truly exists.

III. Research that Describes, Predicts, & Explains Behavior (i.e., cause and effect)

The True Experiment: A research method in which an investigator manipulates one or more factors (independent variables) in order to observe the effect on some behavior or mental process (dependent variable). By randomly assigning participants to groups, other relevant factors are controlled.

Independent Variable: The factor that is being manipulated by the researchers. The theoretical "cause" in the cause and effect relationship.

Dependent Variable: The factor (a behavior or mental process) that is being measured by the researchers. The variable that is predicted to change in response to the manipulation of the IV.

Operational Definitions: Specific statements describing how the IV is manipulated and how the DV is measured.

Random Assignment: Assigning participants to control and experimental conditions on the basis of chance, thus minimizing pre-existing differences between the groups (i.e., it controls preexisting subject variables.

Experimental Condition (or Group): The condition of an experiment that exposes participants to the treatment of interest, that is, to one level of the independent variable.

Control Condition (or Group): The condition of an experiment that contrasts with the experimental condition and serves as a comparison for evaluating the effect of the treatment.

*At the conclusion of an experiment, the mean scores the experimental and control groups receive on the DEPENDENT VARIABLE are COMPARED to determine if a statistically significant difference exists.

Control Techniques used to control confounding variables.

Random Assignment: Controls pre-existing subject variables.

Control Group: Controls history, maturation, and testing effects.

Placebo: An inert substance given to the control group in place of an actual medication. It controls the Placebo Effect.

Double-Blind Design: An experimental procedure in which both the research participants and the research staff are ignorant (blind) about whether subjects are in the control or experimental groups (commonly used in drug-evaluation studies). This type of design controls subject and experimenter effects.

Subject Effects or Biases: Any response by subjects in a study that does not represent how they would normally behave if not under study. Two powerful subject effects are the placebo effect and the demand characteristics of the study.

Demand Characteristics: Aspects of the study that suggest to the subjects what type of behavior is expected or desired by the researchers.

Experimenter Effects or Biases: Any behavior of a researcher that might affect the behavior of the subjects or affect the measurement and recording of the dependent variable.

Ex Post Facto: Designs similar to true experiments, but without all of the control techniques built in (e.g., random assignment may not be used).

Statistics

Measures of Central Tendency

Mean: Arithmetical average calculated by dividing a sum of values by the total number of cases

Median: Point that divides a set of scores in half.

Mode: The most frequent score in a distribution of scores

*Of these three measures, the MEAN is most affected by outliers or extreme scores.

Measures of Variability

Range: Difference between the largest and smallest scores in a distribution.

Variance: A statistical average of the amount of dispersion around the mean in a distribution of the scores. It is the Standard Deviation squared.

Standard Deviation: A statistical measure of the amount of dispersion in a set of scores. Specifically, it is the square root of the average squared deviations from the mean of a set of scores. It is simply the square root of the variance.

*Of the three measures, the RANGE is most affected by outliers.

Distributions of Scores

Normal Curve: Hypothetical, bell-shaped distribution of scores that occurs when a normal distribution is plotted as a frequency polygon.

In a normal distribution, the mean, median, and mode are all equal and divide the distribution in half (the 50th percentile).

Percentile Rank: Reflects the percentage of subjects who score lower than the subject in question

Positively Skewed Distribution: A distribution where most scores are clustered at the lower end of the

curve, with a few very high scores creating a long "tail" to the right. The mean is greater than the median, and the median is greater than the mode.

Negatively Skewed Distribution: A distribution where most scores are clustered at the upper end of the curve, with a few very low scores creating a long "tail" to the left. The mean is less than the median, and the median is less than the mode.