AP Psych Unit 1.3 Vocab

bell curve

Also called the normal curve. Many traits, including intellectual abilities, are said to be normally distributed, with roughly 68 percent of the distribution being within one standard deviation of the mean, and more than 90 percent being within two standard deviations of the mean.

central tendency

A general term for the midpoint, or center, of a distribution. Central tendency can be measured through the mean, median, or mode.

descriptive statistics

Statistics that provide information about the features of a particular sample.

mean

The arithmetic average of all of the scores in a distribution.

median

The middlemost score in a distribution.

mode

The most frequent score in a distribution.

negative (inverse) correlation

A relationship between two variables in which the values of one variable increase as the values of the other variable decrease.

percentile

The percentage of scores in a distribution that are below a particular score.

positive (direct) correlation

A relationship between two variables in which the values of one variable increase as the values of the other variable increase.

standard deviation

A statistic that measures the variability, or degree of spread, of a distribution. It is calculated by taking the square root of the variance, or the average squared deviation of scores from the mean.

statistical significance

A condition in which the difference between the experimental and control groups is so large that it is unlikely to have occurred by chance alone.

variable

Anything that can take on any of a number of values.

variance

A statistic that measures the variability, or degree of spread, in the distribution. It is calculated by taking the average squared deviation of scores from the mean.

z-score

A standardized score with a mean of 0 and a standard deviation of 1. Scores in the distributions of two different measures, such as a measure of IQ and a measure of reading comprehension, are often converted to z-scores so that the distributions can be easily compared with one another.