AP Psychology Module 6-7

control group

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

inferential statistics

numerical data that allow one to generalize - to infer from sample data the probability of something being true of a population

descriptive statistics

numerical data used to measure and describe characteristics of groups. Includes measures of central tendency and measures of variation.

histogram

a bar graph depicting a frequency distribution

standard deviation

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

confounding variable

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

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).

correlation

a measure of the extent to which two variables change together, and thus of how well either variable predicts the other

skewed distribution

a representation of scores that lack symmetry around their average value

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)

correlation coefficient

a statistical index or the relationship between two variables (from -1.0 to +1.0)

statistical significance

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

normal curve (normal distribution)

a symmetrical, bell-shaped curve that describes the distribution of many types of data; most scores fall near the mean and fewer and fewer near the extremes

illusory correlation

the perception of a relationship where none exists

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.

random assignment

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

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.

experimental group

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

mean

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

range

the difference between the highest and lowest scores in a distribution

independent variable

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

validity

the extent to which a test or experiment measures or predicts what it is supposed to

median

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

mode

the most frequently occurring score(s) in a distribution

dependent variable

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