### Sample

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

### Variable

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

### Construct

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

### 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

### Noise

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

### 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

### Experiment

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