range

the difference between the highest and lowest scores in a distribution

control group

in an experiment, the group that is not exposed to the treatment; contrasts with the experimental group and serves as a comparison for evaluating the effect of the treatment

informed consent

an ethical principle that research participants be told enough to enable them to choose whether they wish to participate

median

the middle score in a distribution; half the scores are above it and half are below it

hindsight bias

the tendency to believe, after learning an outcome, that one would have foreseen it AKA: the I-knew-it-all-along phenomenon

random assignment

assigning participants to experimental and control groups by chance, thus minimizing preexisting differences between those assigned to the different groups

random sample

a sample that fairly represents a population because each member has an equal chance of inclusion

placebo effect

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

independent variable

the experimental factor that is manipulated; the variable whose effect is being studied

correlation coefficient

a statistical index of the relationship between two things (from 1 to +1)

critical thinking

thinking that does not blindly accept arguments and conclusions. Rather, it examines assumptions, discerns hidden values, evaluates evidence, and assesses conclusions

operational definition

a statement of the procedures (operations) used to define research variables Example: human intelligence may be operationally defined as “what an intelligence test measures.”

theory

an explanation using an integrated set of principles that organizes observations and predicts behaviors or events

debriefing

the postexperimental explanation of a study, including its purpose and any deceptions, to its participants

naturalistic observation

observing and recording behavior in naturally occurring situations without trying to manipulate and control the situation

confounding variable

a factor other than the independent variable that might produce an effect in an experiment

normal curve

(normal distribution) a symmetrical, bell-shaped curve that describes the distribution of many types of data; most scores fall near the mean, or average (about 68 percent fall within one standard deviation of it) and fewer and fewer near the extremes

scatterplot

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).

standard deviation

a computed measure of how much scores vary around the mean score

correlation

a measure of the extent to which two factors vary together, and thus of how well either factor predicts the other

double-blind procedure

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

dependent variable

the outcome factor; the variable that may change in response to manipulations of the independent variable

hypothesis

a testable prediction, often implied by a a testable prediction, often implied by a theory

experimental group

in an experiment, the group that is exposed to the treatment, that is, to one version of the independent variable

statistical significance

a statistical statement of how likely it is that an obtained result occurred by chance

survey

a technique for ascertaining the self-reported attitudes or behaviors of a particular group, usually by questioning a representative, random sample of the group

population

all the cases in a group being studied, from which samples may be drawn

mode

the most frequently occurring score(s) in a distribution

replication

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

experiment

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 factors

case study

an observation technique in which one person is studied in depth in the hope of revealing universal principles

mean

the arithmetic average of a distribution, obtained by adding the scores and then dividing by the number of scores