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organized sets of concepts that explain phenomena


prediction of how two or more factors are likely to be related


repetition of the methods used in a previous experiment to see whether the same methods will yield the same results

independent variable

the factor that is changed or manipulated during an experiment

dependent variable

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


all the cases in a group, from which samples may be drawn for a study


a subset of the population that participates in the study

random selection

choosing of members of a population so that every individual has an equal chance of being chosen

experimental group

the group that receives the experimental treatment or independent variable

control group

the group that does not receive the experimental treatment or independent variable


a research method in which an investigator manipulates one or more factors to observe the effect on some behavior or mental process; establish cause and effect relationship


a research method that looks like an experiment BUT subjects are not randomly assigned to control and experimental groups; no cause and effect can be drawn

naturalistic observation

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

surveys and tests

obtain large samples of abilities, beliefs, or behaviors at a specific time and place

case study

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

random assignment

division of the sample into groups so that every individual has an equal chance of being put in any group or condition

confounding variable

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

operational definition

a description of the specific procedure used to determine the presence of a variable

experimenter bias

a phenomenon that occurs when a researcher's expectations or preferences about the outcome of a study influence the results obtained

demand characteristics

clues participants discover about the purpose of a study that suggest how they should respond

single blind procedure

research design in which participants don't know whether they are in the experimental or control group

double blind procedure

research design in which neither the experimenter nor the participants know who is in the experimental group and who is in the control group


a physical or psychological treatment that contains no active ingredient but produces an effect because the person receiving it believes it will

placebo effect

response to the belief that the IV will have an effect, rather than the IV's actual effect, which can be a confounding variable


consistency or repeatability of results


the extent to which an instrument measures what it is intended to measure


a branch of mathematics that psychologists use to organize and analyze data

descriptive statistics

numbers that summarize a set of research data obtained from a sample

frequency distribution

an orderly arrangement of scores indicating the frequency of each score or group of scores

central tendency

average or most typical scores of a set or research data or distribution; mean, mode, and median


the arithmetic average of a distribution


the most frequently occurring score in a distribution


the middle number in a set of numbers that are listed in order


the spread or dispersion of a set of research data or distribution; range, variance, standard deviation


the difference between the highest and lowest scores in a distribution

standard deviation

a measure of variability that indicates the average difference between the scores and their mean.

normal distribution

bell-shaped curve that represents data about how lots of human characteristics are dispersed in the population

percentile score

the percentage of scores at or below a certain score

correlation coefficient

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

inferential statistics

statistics that are used to interpret data and draw conclusions

statistical significance

the condition that exists when the probability that the observed findings are due to chance is very low.

ethical guidelines

suggested rules for acting responsibly and morally when conducting research or in clinical practice

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