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Descriptive statistics

organize, summarize, and communicate a group of numerical observations

Inferential statistics

use sample data to make general estimates about the larger population


a set of observations drawn from the population of interest that, it is hoped, share the same characteristics as the population of interest


includes all possible observations about which we'd like to know something


is any observation of a physical, attitudinal, or behavioral characteristic that can take on different values


is a hypothetical idea that is developed (or constructed) to describe and explain human behavior

Discrete observations

can take on only specific values (whole numbers); no other values can exist between these numbers

Continuous observations

can take on a full range of values (numbers out to many decimal points); there is an infinite number of potential values

Nominal variable

is a variable used for observations that have categories, or names, as their values

Ordinal variable

is a variable used for observations that have rankings (1st, 2nd, 3rd...) as their values

Interval variable

is a variable that has numbers as its values; the distance (or interval) between pairs of consecutive numbers is assumed to be equal

Ratio variable

is a variable that meets the criteria for interval variables but also has a meaningful zero point


is a discrete value or condition that a variable can take on

Independent variable

is a variable that we either manipulate or observe to determine its effects on the dependent variable

Dependent variable

is the outcome variable that we hypothesize to be related to, or caused by, changes in the independent variable

Confounding variable

is any variable that systematically co-varies with the independent variable so that we cannot logically determine which variable is at work; also called confound

Extraneous variable

is a randomly distributed influence that detracts from the experimenter's efforts to measure what was intended to be measured


influences an experiment by making the relations between variables less clear than they really are


refers to the consistency of a measure


refers to the extent to which a test actually measures what it was intended to measure

Test-retest reliability

refers to whether the scale being used provides consistent information every time the test is taken

Predictive validity

refers to how well a measuring instrument (such as a personality scale) predicts actual behavior

Hypothesis testing

is the process of drawing conclusions about whether a particular relation between variables is supported by the evidence

Operational definition

specifies the operations or procedures used to measure or manipulate a variable


is a study in which participants are randomly assigned to a condition or level or one or more independent variables

Random assignment

every participant is a study has an equal chance of being assigned to any of the groups, or experimental conditions, in the study

Single-blind experiment

is one in which participants do not know the condition to which they have been assigned. This reduces the possibility that participants will respond as they believe they are expected to respond to a given situation

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