the tendency to believe, after learning an outcome, that one would have foreseen it. (Also known as the I-knew-it-all-along phenomenon.)
thinking that does not blindly accept arguments and conclusions. Rather, it examines assumptions, assesses the source, discerns hidden values, evaluates evidence, and assesses conclusions.
an explanation using an integrated set of principles that organizes observations and predicts behaviors or events.
a testable prediction, often implied by a theory.
a carefully worded statement of the exact procedures (operations) used in a research study. For example, human intelligence may be operationally defined as what an intelligence test measures.
repeating the essence of a research study, usually with different participants in different situations, to see whether the basic finding extends to other participants and circumstances.
a descriptive technique in which one individual or group is studied in depth in the hope of revealing universal principles.
observing and recording behavior in naturally occurring situations without trying to manipulate and control the situation.
a technique for ascertaining the self-reported attitudes or behaviors of a particular group, usually by questioning a representative, random sample of the group.
a flawed sampling process that produces an unrepresentative sample.
all those in a group being studied, from which samples may be drawn. (Note: Except for national studies, this does not refer to a country's whole population.)
a sample that fairly represents a population because each member has an equal chance of inclusion.
a measure of the extent to which two variables change together, and thus of how well either variable predicts the other.
a statistical index of the relationship between two variables (from -1 to +1).
a graphed cluster of dots, each of which represents the values of two variables. The slope of the points suggests the direction of the relationship between the two variables. The amount of scatter suggests the strength of the correlation (little scatter indicates high correlation).
the perception of a relationship where none exists.
a research method in which an investigator manipulates one or more factors (independent variables) to observe the effect on some behavior or mental process (the dependent variable). By random assignment of participants, the experimenter aims to control other relevant variables.
in an experiment, the group exposed to the treatment, that is, to one version of the independent variable.
in an experiment, the group not exposed to the treatment; contrasts with the experimental group and serves as a comparison for evaluating the effect of the treatment.
assigning participants to experimental and control groups by chance, thus minimizing preexisting differences between the different groups.
an experimental procedure in which both the research participants and the research staff are ignorant (blind) about whether the research participants have received the treatment or a placebo. Commonly used in drug-evaluation studies.
the experimental factor that is manipulated; the variable whose effect is being studied.
a factor other than the independent variable that might produce an effect in an experiment.
the outcome factor; the variable that may change in response to manipulations of the independent variable.
the extent to which a test measures or predicts what it is supposed to. (See also content validity and predictive validity.)
numerical data used to measure and describe characteristics of groups. Includes measures of central tendency and measures of variation.
a bar graph depicting a frequency distribution.
the most frequently occurring score(s) in a distribution.
the arithmetic average of a distribution, obtained by adding the scores and then dividing by the number of scores.
the middle score in a distribution; half the scores are above it and half are below it.
a representation of scores that lack symmetry around their average value.
the difference between the highest and lowest scores in a distribution.
a computed measure of how much scores vary around the mean score.
normal curve (normal distribution)
a symmetrical, bell-shaped curve that describes the distribution of many types of data; most scores fall near the mean (about 68 percent fall within one standard deviation of it) and fewer and fewer near the extremes.
numerical data that allow one to generalize—to infer from sample data the probability of something being true of a population.
a statistical statement of how likely it is that an obtained result occurred by chance.
the enduring behaviors, ideas, attitudes, values, and traditions shared by a group of people and transmitted from one generation to the next.
an ethical principle that research participants be told enough to enable them to choose whether they wish to participate.
the postexperimental explanation of a study, including its purpose and any deceptions, to its participants.
experimental results caused by expectations alone; any effect on behavior caused by the administration of an inert substance or condition, which the recipient assumes is an active agent.