After studying Chapter 2, you should know and understand the following key points:

Scientific and Everyday Approaches to Knowledge

The scientific method is empirical and requires systematic, controlled observation.

To achieve control in a research situation, researchers manipulate independent variables or select levels of individual differences variables to determine their effect on behavior.

Dependent variables are measures of behavior used to assess the effects of independent variables.

Scientific reporting is unbiased and objective; clear communication of concepts occurs when operational definitions are used.

Scientific instruments are accurate and precise; physical and psychological measurement should be valid and reliable.

A hypothesis is a tentative explanation for a phenomenon; testable hypotheses have clearly defined concepts (operational definitions), are not circular, and refer to concepts that can be observed.

Scientists adopt a skeptical attitude and are cautious about accepting explanations until sufficient empirical evidence is obtained.

Goals of the Scientific Method

The scientific method is intended to meet four goals: description, prediction, understanding, and creating change.

Psychologists seek to describe events and relationships between variables; most often, researchers use the nomothetic approach and quantitative analysis.

Correlational relationships allow psychologists to predict behavior or events, but do not allow psychologists to infer what causes these relationships.

Psychologists understand the cause of a phenomenon when the three conditions for causal inference are met: covariation, time-order relationship, and elimination of plausible alternative causes.

The experimental method, in which researchers manipulate independent variables to determine their effect on dependent variables, establishes time-order and allows a clearer determination of covariation.

Plausible alternative causes for a relationship are eliminated if there are no confoundings in a study; a study free of confoundings has internal validity.

External validity refers to the extent to which a study's findings may be used to describe different populations, settings, and conditions.

Psychologists apply their knowledge and research methods to change people's lives for the better.

Scientific Theory Construction and Testing

Theories are proposed explanations for the causes of behavior and vary in their scope and level of explanation.

A scientific theory is a logically organized set of propositions that defines events, describes relationships among events, and explains the occurrence of events.

Successful scientific theories organize empirical knowledge, guide research by offering testable hypotheses, and survive rigorous testing.

Researchers evaluate theories by judging the theory's internal consistency, observing whether hypothesized outcomes occur when the theory is tested, and noting whether the theory makes precise predictions based on parsimonious explanations.