Chapter 2: Frequency Distributions

Frequency Distribution

an organized tabulation of the number of individuals located in each category on the scale of measurement

Range

the distance from the upper real limit of the highest score to the lower real limit of the lowest score; the total distance from the absolute highest point to the lowest point in the distribution

Grouped Frequency Distribution

a frequency distribution where scores are grouped into intervals rather than listed as individual values

Class Interval

a group of scores in a grouped frequency distribution

Apparent Limits

the score values that appear as the lowest score and the highest score in an interval

Histogram

a graph showing a bar above each score or interval so that the height of the bar corresponds to the frequency and width extends to the real limits

Polygon

a graph consisting of a line that connects a series of dots; a dot is placed above each score or interval so that the height of the dot corresponds to the frequency

Bar Graph

a graph showing a bar above each score or interval so that the height of the bar corresponds to the frequency; a space is left between adjacent bars

Relative Frequency

the proportion of the total distribution rather than the absolute frequency; used for population distributions for which the absolute number of individuals is not known for each category

Symmetrical Distribution

the possibility to draw a vertical line through the middle so that one side of the distribution is a mirror image of the other

Tail(s) of a Distribution

a section on either side of a distribution where the frequency tapers down toward zero as the X values become more extreme

Positively Skewed Distribution

a distribution where the scores pile up on the left side and taper off to the right

Negatively Skewed Distribution

a distribution where the scores pile up on the right side and taper off to the left

Percentile

a score identified by its percentile rank

Percentile Rank

the percentage of individuals in the distribution with scores at or below the particular value

Cumulative Frequency (cf)

the total of frequencies

Cumulative Percentage (c%)

the percentage of the cumulative frequency within each interval; a method for estimating a value between points in a data set

Interpolation

a method for estimating a value between points in a data set

Stem and Leaf Display

a device for presenting quantitative data in a graphical format, similar to a histogram