Ch 5 Vocab

Frequency Distribution A table in which all of the scores are listed along with the frequency with which each occurs. class interval frequency distribution A table in which the scores are grouped into intervals and listed along with the frequency of scores in each interval. qualitative variable discrete variable.

a categorical variable for which each value represents a

Bar Graph A graphical representation of a frequency distribution in which vertical bars are centered above each category along the x-axis and are separated from each other by a space, indicating that the levels of the variable represent distinct, unrelated categories. Quantitative Variable quantity

A variable for which the scores represent a change in

histogram a graphical representation of a frequency distribution in which vertical bars centered above scores on the x-axis touch each other to indicate that the scores on the variable represent related, increasing values. Frequency Polygon scores.

A line graph of the frequencies of individual

Descriptive Statistics Numerical measures that describe a distribution by providing information on the central tendency of the distribution, and the shape of the distribution. Measure of Central Tendency "middleness" of a an entire distribution.

A number that characterizes the

Mean A measure of central tendency; the arithmetic average of a distribution. Only used with interval and ratio data. Median A measure of central tendency; the middle score in a distribution after the scores have been arranged from highest to lowest or lowest to highest. Only used with Ordinal, interval, and ratio data. Mode A measure of central tendency; the score in a distribution that occurs with the greatest frequency. Used with Nominal, ordinal, interval, or ratio data. Range A measure of variation; the difference between the lowest and highest scores in a distribution.

Standard Deviation A measure of variation; the average difference between the scores in the distribution and the mean or central point of the distribution, or more precisely, the square root of the average squared deviation from the mean. Average Deviation An alternative measure of variation that, like the standard deviation, indicates the average difference between the scores in a distribution and the mean of the distribution. Variance

The standard deviation squared.

Normal Curve A symmetrical, bell-shaped frequency polygon representing a normal distribution. Normal Distribution A theoretical frequency distribution that has certain special characteristics. (1) it's bell shaped and symmetrical - the right half is a mirror image of the left half. (2) the mean, median, and mode are located at the center of the distribution. (3) unimodal (4) most observations are clustered around the center of distribution with fewer observations at the ends or "tails" of the distribution. Kurtosis

how flat or peaked a normal distribution is

Mesokurtic curves that have peaks of medium height, and the distributions are moderate in breadth. Leptokurtic Cure that are tall and thin, with only a few scores in the middle of the distribution having a high frequency. Platykurtic

Curves that are short and more dispersed

Positively Skewed Distribution A distribution in which the peak is to the left of the center point, and the tail extends toward the right, or in the positive direction. Negatively Skewed Distribution A distribution in which the peak is to the right of the center point, and the tail extends toward the left, or in the negative direction. Z-score A number that indicates how many deviation units a raw score is from the mean of a distribution. Standard Normal Distribution standard deviation of 1. Probability

A normal distribution with a mean of 0 and a

The expected relative frequency of a particular outcome.

Percentile Rank A score that indicates the percentage of people who scored at or below a given raw score.