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