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Scientific Method

A five-step process for empirical investigation of a hypothesis under conditions designed to control biases and subjective judgments

Empirical Investigation

Approach to research that relies on sensory experience and observation as research data


Testable explanation for a set of facts or observations. In science, a theory is not just speculation or a guess


A statement predicting the outcome of a scientific study; a statement describing the relationship among variables of a study

Operational Definition

Specific descriptions of concepts involving the conditions of a scientific study; stated in terms of how the concepts are to be measured or what operations are being employed

Independent Variable

Stimulus condition so named because the experimenter changes it independently of all the other carefully controlled experimental conditions

Random Presentation

A process by which chance alone determines the order in which the stimulus is presented


Pieces of information. Information gathered by a researcher to be used in testing a hypothesis

Dependent Variable

The measure outcome of a study; the responses of the subjects in a study


Doing a study over to see whether the same results are obtained


Research in which the researcher controls all the conditions and directly manipulates the conditions, including the independent variable

Confounding/extraneous variables

Variables that have an unwanted influence on the outcome of an experiment


Constraints that the experimenter places on the experiment to ensure that each subject has the exact same conditions

Random Assignment

Each subject of the sample has an equal likelihood of being chosen for the experiment group of an experiment

Ex Post Facto

Research in which we choose subjects based on a pre-existing condition

Correlational Study

Type of research that is mainly statistical in nature. Determines the relationship between two variables


Quasi-experimental method in which questions are asked to subjects. Questions must not be skewed or biased

Naturalistic Observation

Research method in which subjects are observed in their natural environment

Longitudinal Study

Type of study in which one group of subjects is followed an observed for an extended period of time

Cross-Sectional Study

Study in which a representative cross-section of the population is tested or surveyed at one specific time

Cohort-Sequential Study

Research method in which a cross section of the population is chosen and then each cohort is followed for a short period of time

Personal Bias

Researcher allowing personal beliefs to affect the outcome of a study

Expectancy Bias

Researcher allowing his or her expectations to affect the outcome of a study

Double-Blind Study

Experimental procedure in which both researchers and participants are uninformed about the nature of the independent variable being administered

Institutional Review Board(IRB)

Committee at each institution where research is conducted to review every experiment for ethics and methodology

Institutional Animal Care and Use Committee

A committee at each institution where research is conducted to review every experiment involving animals for ethics and methodology

ABC'S of Laboratory Animal Research

All animal research must comply with ABC's of laboratory animal research; appropriate, beneficial, and caring

Frequency Distribution

Summary chart showing how frequently each of the various scores in a set of data occurs


Bar graph depicting a frequency distribution. The height of the bars indicates the frequency of a group of scores

Descriptive Statistics

Statistical procedures used to describe characteristics and responses of groups of subjects


Measure of central tendency most often used to describe a set of data-- calculated by adding all the scores and dividing by the number of scores


A measure of central tendency for a distribution, represented by the score that separates the upper half of the scores in a distribution from the lower half


Measure of central tendency for a distribution, represented by the score that occurs more often than any other


Simplest measure of variability represented by the difference between the highest and the lowest values in a frequency distribution

Standard Deviation

Measure of variability that indicates the average difference between the scores and their mean


Relationship between variables in which changes in one variable-- as in the correlation between a child's age and height

Normal Distribution

Bell-shaped curve, describing the spread of a characteristic throughout a population

Correlation Coefficient

Number between -1 and +1 expressing the degree of relationship between two variables

Inferential Statistics

Statistical techniques used to assess whether the results of a study are reliable or whether they might be simply the result of chance. Often used to determine whether two or more groups are essentially the same or different

Random Sample

Sample group of subjects selected by chance

Representative Sample

Sample obtained in a such a way that it reflects the distribution of important variables in the larger population in which the researchers are interested- variables such as age, income level, ethnicity, and geographic distribution

Significant Difference

Psychologists accept difference between the groups as "real" or significant, when the probability that it might be to due to an atypical sample drawn by chance is less than 5 in 100

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