sample

the small group of participants, out of the total number available, that a researcher studies

naturalistic observation

research method in which the psychologist observes the subject in a natural setting without interfering

case study

research method that involves an intensive investigation of one or more participants

survey

research method in which information is obtained by asking many individuals a fixed set of questions

longitudinal study

research method in which data is collected about a group of participants over a number of years to assess how certain characteristics change or remain the same during development

cross-sectional study

research method in which data is collected from groups of participants of different ages and compared so that conclusions can be drawn about differences due to age

correlation

the measure of a relationship between two variables or sets of data

hypothesis

an educated guess that attempts to explain an observation or answer a question

variable

any factor that is capable of change

experimental group

the group to which an independent variable is applied

control group

the group that is treated in the same way as the experimental group except that the experimental treatment (the independent variable) is not applied

self-fulfilling prophecy

a situation in which a researcher's expectations influence that person's own behavior, and thereby influence the participant's behavior

single-blind experiment

an experiment in which the participants are unaware of which participants received the treatment

double-blind experiment

an experiment in which neither the experimenter nor the participants know which participants received which treatment

placebo effect

a change in a participant's illness or behavior that results from a belief that the treatment will have an effect, rather than the actual treatment

statistics

a branch of applied mathematics concerned with the collection and interpretation of quantitative data and the use of probability theory to estimate population parameters

descriptive statistics

the listing and summarizing of data in a practical, efficient way

frequency distribution

an arrangement of data that indicates how often a particular score or observation occurs

normal curve

a graph of frequency distribution shaped like a symmetrical, bell-shaped curve; a graph of normal distribution

central tendency

a number that describes something about the "average" score of a distribution

variance

a measure of difference, or variance

standard deviation

a measure of variability that describes an average distance of every score from the mean

correlation coefficient

describes the direction and strength of the relationship between two sets of variables

inferential statistics

numerical methods used to determine whether research data support a hypothesis or whether results were due to chance