Statistics Chapter 2

Graphical summaries for qualitative data & frequency distributions and their graphs

frequency

the number of times a category occurs in a data set

frequency distribution

a table that presents the frequency for each category

relative frequency distribution

represents the proportion of observations in a category, the frequency of the category divided by the sum of all frequencies

bar graph

a graphical representation of a frequency distribution,

classes

intervals of data with equal width that cover all the values that are observed

lower class limit

the smallest value that can appear in that class, ex. class: 50-99, answer is 50

upper class limit

the highest value that can appear in that class, ex. class: 50-99, answer is 99

class width

the difference between consecutive lower class limits, largest data value - smallest data value / number of classes

histograms

relative frequency distribution put into graphical form

open-ended classes

when a class has either no upper class limit or no lower class limit, ex. 85 or older

skewed to the right

histogram with a long right hand tail, or positively skewed

skewed to the left

histogram with a long left hand tail, or negatively skewed

modes

a peak or high point of a histogram, unimodal or bimodal

frequency polygraph

displays the shape of a distibution

class midpoint

the average of a class lower limit and the next class lower limit, lower limit + next class lower limit / 2